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 $167.88   9.671%   $184.1157   $184.12   $184.10   $184.10  
  Purchase #2 $102.99   13.241%   $116.6269   $116.63   $116.65   $116.60  
  Purchase #3 $49.60   12.850%   $55.9736   $55.97   $55.95   $56.00  
  Purchase #4 $85.58   7.247%   $91.782   $91.78   $91.80   $91.80  
  Purchase #5 $202.50   12.226%   $227.2577   $227.26   $227.25   $227.30  
  Purchase #6 $110.42   7.126%   $118.2885   $118.29   $118.30   $118.30  
  Purchase #7 $107.44   7.610%   $115.6162   $115.62   $115.60   $115.60  
  7 purchase totals = $826.41       $909.6606   $909.67   $909.65   $909.70