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 $177.80   10.817%   $197.0326   $197.03   $197.05   $197.00  
  Purchase #2 $146.46   9.499%   $160.3722   $160.37   $160.35   $160.40  
  Purchase #3 $167.36   12.799%   $188.7804   $188.78   $188.80   $188.80  
  Purchase #4 $234.31   3.578%   $242.6936   $242.69   $242.70   $242.70  
  Purchase #5 $199.40   5.498%   $210.363   $210.36   $210.35   $210.40  
  Purchase #6 $240.61   9.763%   $264.1008   $264.10   $264.10   $264.10  
  Purchase #7 $34.57   13.735%   $39.3182   $39.32   $39.30   $39.30  
  7 purchase totals = $1,200.51       $1,302.6608   $1,302.65   $1,302.65   $1,302.70