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 $124.81   7.512%   $134.1857   $134.19   $134.20   $134.20  
  Purchase #2 $228.36   8.568%   $247.9259   $247.93   $247.95   $247.90  
  Purchase #3 $196.98   3.276%   $203.4331   $203.43   $203.45   $203.40  
  Purchase #4 $10.32   3.450%   $10.676   $10.68   $10.70   $10.70  
  Purchase #5 $13.92   10.619%   $15.3982   $15.40   $15.40   $15.40  
  Purchase #6 $212.54   9.387%   $232.4911   $232.49   $232.50   $232.50  
  Purchase #7 $102.25   8.180%   $110.6141   $110.61   $110.60   $110.60  
  7 purchase totals = $889.18       $954.7241   $954.73   $954.80   $954.70