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 $30.80   5.822%   $32.5932   $32.59   $32.60   $32.60  
  Purchase #2 $97.50   9.364%   $106.6299   $106.63   $106.65   $106.60  
  Purchase #3 $228.34   11.487%   $254.5694   $254.57   $254.55   $254.60  
  Purchase #4 $194.76   13.622%   $221.2902   $221.29   $221.30   $221.30  
  Purchase #5 $162.34   6.781%   $173.3483   $173.35   $173.35   $173.30  
  Purchase #6 $169.56   12.226%   $190.2904   $190.29   $190.30   $190.30  
  Purchase #7 $181.94   11.748%   $203.3143   $203.31   $203.30   $203.30  
  7 purchase totals = $1,065.24       $1,182.0357   $1,182.03   $1,182.05   $1,182.00