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 $151.66   8.814%   $165.0273   $165.03   $165.05   $165.00  
  Purchase #2 $167.39   11.632%   $186.8608   $186.86   $186.85   $186.90  
  Purchase #3 $117.86   11.700%   $131.6496   $131.65   $131.65   $131.60  
  Purchase #4 $32.36   6.752%   $34.5449   $34.54   $34.55   $34.50  
  Purchase #5 $109.79   10.350%   $121.1533   $121.15   $121.15   $121.20  
  Purchase #6 $189.26   6.487%   $201.5373   $201.54   $201.55   $201.50  
  Purchase #7 $107.97   11.733%   $120.6381   $120.64   $120.65   $120.60  
  7 purchase totals = $876.29       $961.4113   $961.41   $961.45   $961.30