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 $186.39   8.152%   $201.5845   $201.58   $201.60   $201.60  
  Purchase #2 $81.55   6.753%   $87.0571   $87.06   $87.05   $87.10  
  Purchase #3 $41.96   5.456%   $44.2493   $44.25   $44.25   $44.20  
  Purchase #4 $199.81   13.631%   $227.0461   $227.05   $227.05   $227.00  
  Purchase #5 $76.59   11.384%   $85.309   $85.31   $85.30   $85.30  
  Purchase #6 $114.56   12.283%   $128.6314   $128.63   $128.65   $128.60  
  Purchase #7 $60.79   5.682%   $64.2441   $64.24   $64.25   $64.20  
  7 purchase totals = $761.65       $838.1215   $838.12   $838.15   $838.00