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 $24.41   4.813%   $25.5849   $25.58   $25.60   $25.60  
  Purchase #2 $71.52   6.414%   $76.1073   $76.11   $76.10   $76.10  
  Purchase #3 $222.89   5.529%   $235.2136   $235.21   $235.20   $235.20  
  Purchase #4 $11.49   6.109%   $12.1919   $12.19   $12.20   $12.20  
  Purchase #5 $161.47   6.355%   $171.7314   $171.73   $171.75   $171.70  
  Purchase #6 $203.45   12.296%   $228.4662   $228.47   $228.45   $228.50  
  Purchase #7 $53.41   4.310%   $55.712   $55.71   $55.70   $55.70  
  7 purchase totals = $748.64       $805.0073   $805.00   $805.00   $805.00