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 $145.48   10.398%   $160.607   $160.61   $160.60   $160.60  
  Purchase #2 $133.40   12.184%   $149.6535   $149.65   $149.65   $149.70  
  Purchase #3 $53.33   5.725%   $56.3831   $56.38   $56.40   $56.40  
  Purchase #4 $244.60   9.455%   $267.7269   $267.73   $267.75   $267.70  
  Purchase #5 $230.66   13.319%   $261.3816   $261.38   $261.40   $261.40  
  Purchase #6 $202.91   11.168%   $225.571   $225.57   $225.55   $225.60  
  Purchase #7 $129.59   10.637%   $143.3745   $143.37   $143.35   $143.40  
  7 purchase totals = $1,139.97       $1,264.6976   $1,264.69   $1,264.70   $1,264.80