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 $245.35   9.173%   $267.856   $267.86   $267.85   $267.90  
  Purchase #2 $57.83   13.753%   $65.7834   $65.78   $65.80   $65.80  
  Purchase #3 $69.30   11.782%   $77.4649   $77.46   $77.45   $77.50  
  Purchase #4 $133.96   13.390%   $151.8972   $151.90   $151.90   $151.90  
  Purchase #5 $112.86   7.624%   $121.4644   $121.46   $121.45   $121.50  
  Purchase #6 $83.81   11.757%   $93.6635   $93.66   $93.65   $93.70  
  Purchase #7 $24.33   12.829%   $27.4513   $27.45   $27.45   $27.50  
  7 purchase totals = $727.44       $805.5807   $805.57   $805.55   $805.80