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 $156.67   6.873%   $167.4379   $167.44   $167.45   $167.40  
  Purchase #2 $118.59   4.288%   $123.6751   $123.68   $123.70   $123.70  
  Purchase #3 $148.79   4.223%   $155.0734   $155.07   $155.05   $155.10  
  Purchase #4 $249.47   7.754%   $268.8139   $268.81   $268.80   $268.80  
  Purchase #5 $134.57   11.629%   $150.2191   $150.22   $150.20   $150.20  
  Purchase #6 $44.79   5.143%   $47.0935   $47.09   $47.10   $47.10  
  Purchase #7 $11.45   13.622%   $13.0097   $13.01   $13.00   $13.00  
  7 purchase totals = $864.33       $925.3226   $925.32   $925.30   $925.30