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 $150.70   4.118%   $156.9058   $156.91   $156.90   $156.90  
  Purchase #2 $56.98   5.491%   $60.1088   $60.11   $60.10   $60.10  
  Purchase #3 $89.32   5.378%   $94.1236   $94.12   $94.10   $94.10  
  Purchase #4 $210.84   11.740%   $235.5926   $235.59   $235.60   $235.60  
  Purchase #5 $59.74   9.760%   $65.5706   $65.57   $65.55   $65.60  
  Purchase #6 $123.93   12.841%   $139.8439   $139.84   $139.85   $139.80  
  Purchase #7 $70.56   4.242%   $73.5532   $73.55   $73.55   $73.60  
  7 purchase totals = $762.07       $825.6985   $825.69   $825.65   $825.70