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 $153.28   10.266%   $169.0157   $169.02   $169.00   $169.00  
  Purchase #2 $155.71   3.365%   $160.9496   $160.95   $160.95   $160.90  
  Purchase #3 $54.85   11.560%   $61.1907   $61.19   $61.20   $61.20  
  Purchase #4 $124.89   3.302%   $129.0139   $129.01   $129.00   $129.00  
  Purchase #5 $202.93   13.174%   $229.664   $229.66   $229.65   $229.70  
  Purchase #6 $33.42   3.371%   $34.5466   $34.55   $34.55   $34.50  
  Purchase #7 $214.90   5.405%   $226.5153   $226.52   $226.50   $226.50  
  7 purchase totals = $939.98       $1,010.8958   $1,010.90   $1,010.85   $1,010.80