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 $197.78   13.639%   $224.7552   $224.76   $224.75   $224.80  
  Purchase #2 $236.32   4.422%   $246.7701   $246.77   $246.75   $246.80  
  Purchase #3 $75.66   10.609%   $83.6868   $83.69   $83.70   $83.70  
  Purchase #4 $211.45   8.190%   $228.7678   $228.77   $228.75   $228.80  
  Purchase #5 $136.52   12.184%   $153.1536   $153.15   $153.15   $153.20  
  Purchase #6 $175.87   13.484%   $199.5843   $199.58   $199.60   $199.60  
  Purchase #7 $62.59   3.517%   $64.7913   $64.79   $64.80   $64.80  
  7 purchase totals = $1,096.19       $1,201.5091   $1,201.51   $1,201.50   $1,201.70