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 $203.61   10.783%   $225.5653   $225.57   $225.55   $225.60  
  Purchase #2 $227.66   4.402%   $237.6816   $237.68   $237.70   $237.70  
  Purchase #3 $23.53   9.296%   $25.7173   $25.72   $25.70   $25.70  
  Purchase #4 $234.93   13.801%   $267.3527   $267.35   $267.35   $267.40  
  Purchase #5 $232.96   6.375%   $247.8112   $247.81   $247.80   $247.80  
  Purchase #6 $226.84   9.202%   $247.7138   $247.71   $247.70   $247.70  
  Purchase #7 $103.36   12.234%   $116.0051   $116.01   $116.00   $116.00  
  7 purchase totals = $1,252.89       $1,367.8470   $1,367.85   $1,367.80   $1,367.90