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 $78.32   6.464%   $83.3826   $83.38   $83.40   $83.40  
  Purchase #2 $162.93   4.690%   $170.5714   $170.57   $170.55   $170.60  
  Purchase #3 $160.43   8.554%   $174.1532   $174.15   $174.15   $174.20  
  Purchase #4 $84.38   9.820%   $92.6661   $92.67   $92.65   $92.70  
  Purchase #5 $108.37   8.654%   $117.7483   $117.75   $117.75   $117.70  
  Purchase #6 $249.87   8.336%   $270.6992   $270.70   $270.70   $270.70  
  Purchase #7 $126.29   6.626%   $134.658   $134.66   $134.65   $134.70  
  7 purchase totals = $970.59       $1,043.8788   $1,043.88   $1,043.85   $1,044.00