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 $119.53   6.220%   $126.9648   $126.96   $126.95   $127.00  
  Purchase #2 $197.77   3.495%   $204.6821   $204.68   $204.70   $204.70  
  Purchase #3 $8.89   9.349%   $9.7211   $9.72   $9.70   $9.70  
  Purchase #4 $241.46   12.603%   $271.8912   $271.89   $271.90   $271.90  
  Purchase #5 $247.38   13.732%   $281.3502   $281.35   $281.35   $281.40  
  Purchase #6 $179.65   8.122%   $194.2412   $194.24   $194.25   $194.20  
  Purchase #7 $246.35   11.584%   $274.8872   $274.89   $274.90   $274.90  
  7 purchase totals = $1,241.03       $1,363.7378   $1,363.73   $1,363.75   $1,363.80