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 $97.71   5.149%   $102.7411   $102.74   $102.75   $102.70  
  Purchase #2 $179.41   4.160%   $186.8735   $186.87   $186.85   $186.90  
  Purchase #3 $48.36   7.871%   $52.1664   $52.17   $52.15   $52.20  
  Purchase #4 $226.56   6.356%   $240.9602   $240.96   $240.95   $241.00  
  Purchase #5 $29.98   3.588%   $31.0557   $31.06   $31.05   $31.10  
  Purchase #6 $228.78   3.506%   $236.801   $236.80   $236.80   $236.80  
  Purchase #7 $89.34   7.428%   $95.9762   $95.98   $96.00   $96.00  
  7 purchase totals = $900.14       $946.5741   $946.58   $946.55   $946.70