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 $216.92   13.501%   $246.2064   $246.21   $246.20   $246.20  
  Purchase #2 $199.97   6.687%   $213.342   $213.34   $213.35   $213.30  
  Purchase #3 $149.54   11.661%   $166.9779   $166.98   $167.00   $167.00  
  Purchase #4 $157.52   3.471%   $162.9875   $162.99   $163.00   $163.00  
  Purchase #5 $59.94   6.375%   $63.7612   $63.76   $63.75   $63.80  
  Purchase #6 $68.85   5.738%   $72.8006   $72.80   $72.80   $72.80  
  Purchase #7 $110.27   12.415%   $123.96   $123.96   $123.95   $124.00  
  7 purchase totals = $963.01       $1,050.0356   $1,050.04   $1,050.05   $1,050.10