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 $202.56   11.676%   $226.2109   $226.21   $226.20   $226.20  
  Purchase #2 $43.43   6.179%   $46.1135   $46.11   $46.10   $46.10  
  Purchase #3 $93.70   7.283%   $100.5242   $100.52   $100.50   $100.50  
  Purchase #4 $105.92   4.390%   $110.5699   $110.57   $110.55   $110.60  
  Purchase #5 $64.34   12.689%   $72.5041   $72.50   $72.50   $72.50  
  Purchase #6 $95.76   11.288%   $106.5694   $106.57   $106.55   $106.60  
  Purchase #7 $237.64   11.639%   $265.2989   $265.30   $265.30   $265.30  
  7 purchase totals = $843.35       $927.7909   $927.78   $927.70   $927.80