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 $179.50   8.333%   $194.4577   $194.46   $194.45   $194.50  
  Purchase #2 $224.92   7.872%   $242.6257   $242.63   $242.65   $242.60  
  Purchase #3 $244.38   10.133%   $269.143   $269.14   $269.15   $269.10  
  Purchase #4 $96.45   11.611%   $107.6488   $107.65   $107.65   $107.60  
  Purchase #5 $78.83   7.533%   $84.7683   $84.77   $84.75   $84.80  
  Purchase #6 $106.75   6.619%   $113.8158   $113.82   $113.80   $113.80  
  Purchase #7 $188.53   7.592%   $202.8432   $202.84   $202.85   $202.80  
  7 purchase totals = $1,119.36       $1,215.3025   $1,215.31   $1,215.30   $1,215.20