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 $168.68   10.850%   $186.9818   $186.98   $187.00   $187.00  
  Purchase #2 $101.79   3.821%   $105.6794   $105.68   $105.70   $105.70  
  Purchase #3 $77.33   12.563%   $87.045   $87.05   $87.05   $87.00  
  Purchase #4 $68.58   9.490%   $75.0882   $75.09   $75.10   $75.10  
  Purchase #5 $206.85   5.254%   $217.7179   $217.72   $217.70   $217.70  
  Purchase #6 $169.67   10.763%   $187.9316   $187.93   $187.95   $187.90  
  Purchase #7 $164.82   12.727%   $185.7966   $185.80   $185.80   $185.80  
  7 purchase totals = $957.72       $1,046.2405   $1,046.25   $1,046.30   $1,046.20