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 $243.47   7.437%   $261.5769   $261.58   $261.60   $261.60  
  Purchase #2 $122.79   9.783%   $134.8025   $134.80   $134.80   $134.80  
  Purchase #3 $216.53   7.409%   $232.5727   $232.57   $232.55   $232.60  
  Purchase #4 $111.76   11.735%   $124.875   $124.88   $124.90   $124.90  
  Purchase #5 $195.78   4.320%   $204.2377   $204.24   $204.25   $204.20  
  Purchase #6 $19.77   13.182%   $22.3761   $22.38   $22.40   $22.40  
  Purchase #7 $149.38   3.692%   $154.8951   $154.90   $154.90   $154.90  
  7 purchase totals = $1,059.48       $1,135.3360   $1,135.35   $1,135.40   $1,135.40