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 $195.76   3.841%   $203.2791   $203.28   $203.30   $203.30  
  Purchase #2 $58.48   11.176%   $65.0157   $65.02   $65.00   $65.00  
  Purchase #3 $66.41   5.490%   $70.0559   $70.06   $70.05   $70.10  
  Purchase #4 $163.52   7.385%   $175.596   $175.60   $175.60   $175.60  
  Purchase #5 $108.76   13.349%   $123.2784   $123.28   $123.30   $123.30  
  Purchase #6 $45.51   4.717%   $47.6567   $47.66   $47.65   $47.70  
  Purchase #7 $125.94   5.435%   $132.7848   $132.78   $132.80   $132.80  
  7 purchase totals = $764.38       $817.6666   $817.68   $817.70   $817.80