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 $96.38   12.269%   $108.2049   $108.20   $108.20   $108.20  
  Purchase #2 $180.56   13.729%   $205.3491   $205.35   $205.35   $205.30  
  Purchase #3 $194.43   5.173%   $204.4879   $204.49   $204.50   $204.50  
  Purchase #4 $119.89   5.582%   $126.5823   $126.58   $126.60   $126.60  
  Purchase #5 $235.38   6.615%   $250.9504   $250.95   $250.95   $251.00  
  Purchase #6 $242.58   9.146%   $264.7664   $264.77   $264.75   $264.80  
  Purchase #7 $45.46   8.443%   $49.2982   $49.30   $49.30   $49.30  
  7 purchase totals = $1,114.68       $1,209.6392   $1,209.64   $1,209.65   $1,209.70