Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $226.85   11.511%   $252.9627   $252.96   $252.95   $253.00  
  Purchase #2 $195.86   7.808%   $211.1527   $211.15   $211.15   $211.20  
  Purchase #3 $100.97   7.645%   $108.6892   $108.69   $108.70   $108.70  
  Purchase #4 $138.54   6.197%   $147.1253   $147.13   $147.15   $147.10  
  Purchase #5 $187.93   8.545%   $203.9886   $203.99   $204.00   $204.00  
  Purchase #6 $119.31   3.506%   $123.493   $123.49   $123.50   $123.50  
  Purchase #7 $154.52   8.278%   $167.3112   $167.31   $167.30   $167.30  
  7 purchase totals = $1,123.98       $1,214.7227   $1,214.72   $1,214.75   $1,214.80