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 $76.97   13.430%   $87.3071   $87.31   $87.30   $87.30  
  Purchase #2 $157.61   8.274%   $170.6507   $170.65   $170.65   $170.70  
  Purchase #3 $190.69   13.775%   $216.9575   $216.96   $216.95   $217.00  
  Purchase #4 $158.80   11.691%   $177.3653   $177.37   $177.35   $177.40  
  Purchase #5 $62.65   8.538%   $67.9991   $68.00   $68.00   $68.00  
  Purchase #6 $43.87   9.598%   $48.0806   $48.08   $48.10   $48.10  
  Purchase #7 $219.26   11.453%   $244.3718   $244.37   $244.35   $244.40  
  7 purchase totals = $909.85       $1,012.7321   $1,012.74   $1,012.70   $1,012.90