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 $58.81   8.700%   $63.9265   $63.93   $63.95   $63.90  
  Purchase #2 $210.35   8.462%   $228.1498   $228.15   $228.15   $228.10  
  Purchase #3 $49.72   4.506%   $51.9604   $51.96   $51.95   $52.00  
  Purchase #4 $214.79   11.783%   $240.0987   $240.10   $240.10   $240.10  
  Purchase #5 $135.35   3.298%   $139.8138   $139.81   $139.80   $139.80  
  Purchase #6 $20.38   4.770%   $21.3521   $21.35   $21.35   $21.40  
  Purchase #7 $77.69   3.256%   $80.2196   $80.22   $80.20   $80.20  
  7 purchase totals = $767.09       $825.5209   $825.52   $825.50   $825.50