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 $119.66   11.231%   $133.099   $133.10   $133.10   $133.10  
  Purchase #2 $193.36   5.199%   $203.4128   $203.41   $203.40   $203.40  
  Purchase #3 $211.34   5.841%   $223.6844   $223.68   $223.70   $223.70  
  Purchase #4 $35.46   13.570%   $40.2719   $40.27   $40.25   $40.30  
  Purchase #5 $203.55   9.747%   $223.39   $223.39   $223.40   $223.40  
  Purchase #6 $94.38   8.689%   $102.5807   $102.58   $102.60   $102.60  
  Purchase #7 $210.73   11.717%   $235.4212   $235.42   $235.40   $235.40  
  7 purchase totals = $1,068.48       $1,161.8600   $1,161.85   $1,161.85   $1,161.90