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 $106.75   6.563%   $113.756   $113.76   $113.75   $113.80  
  Purchase #2 $164.36   8.387%   $178.1449   $178.14   $178.15   $178.10  
  Purchase #3 $94.44   10.431%   $104.291   $104.29   $104.30   $104.30  
  Purchase #4 $103.59   3.424%   $107.1369   $107.14   $107.15   $107.10  
  Purchase #5 $201.33   8.802%   $219.0511   $219.05   $219.05   $219.10  
  Purchase #6 $35.97   9.802%   $39.4958   $39.50   $39.50   $39.50  
  Purchase #7 $77.74   9.368%   $85.0227   $85.02   $85.00   $85.00  
  7 purchase totals = $784.18       $846.8984   $846.90   $846.90   $846.90