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 $237.63   12.756%   $267.9421   $267.94   $267.95   $267.90  
  Purchase #2 $202.91   11.213%   $225.6623   $225.66   $225.65   $225.70  
  Purchase #3 $53.73   5.753%   $56.8211   $56.82   $56.80   $56.80  
  Purchase #4 $191.94   5.311%   $202.1339   $202.13   $202.15   $202.10  
  Purchase #5 $170.46   6.694%   $181.8706   $181.87   $181.85   $181.90  
  Purchase #6 $112.37   8.596%   $122.0293   $122.03   $122.05   $122.00  
  Purchase #7 $178.35   7.107%   $191.0253   $191.03   $191.05   $191.00  
  7 purchase totals = $1,147.39       $1,247.4846   $1,247.48   $1,247.50   $1,247.40