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 $61.49   13.355%   $69.702   $69.70   $69.70   $69.70  
  Purchase #2 $236.69   12.601%   $266.5153   $266.52   $266.50   $266.50  
  Purchase #3 $14.74   4.118%   $15.347   $15.35   $15.35   $15.30  
  Purchase #4 $78.97   11.464%   $88.0231   $88.02   $88.00   $88.00  
  Purchase #5 $134.47   12.418%   $151.1685   $151.17   $151.15   $151.20  
  Purchase #6 $174.95   4.774%   $183.3021   $183.30   $183.30   $183.30  
  Purchase #7 $86.44   9.570%   $94.7123   $94.71   $94.70   $94.70  
  7 purchase totals = $787.75       $868.7703   $868.77   $868.70   $868.70