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 $118.63   6.501%   $126.3421   $126.34   $126.35   $126.30  
  Purchase #2 $145.31   9.862%   $159.6405   $159.64   $159.65   $159.60  
  Purchase #3 $184.67   9.452%   $202.125   $202.13   $202.15   $202.10  
  Purchase #4 $155.42   12.785%   $175.2904   $175.29   $175.30   $175.30  
  Purchase #5 $85.52   3.415%   $88.4405   $88.44   $88.45   $88.40  
  Purchase #6 $215.37   11.613%   $240.3809   $240.38   $240.40   $240.40  
  Purchase #7 $40.29   8.609%   $43.7586   $43.76   $43.75   $43.80  
  7 purchase totals = $945.21       $1,035.9780   $1,035.98   $1,036.05   $1,035.90