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 $153.85   6.347%   $163.6149   $163.61   $163.60   $163.60  
  Purchase #2 $196.98   11.287%   $219.2131   $219.21   $219.20   $219.20  
  Purchase #3 $183.66   12.454%   $206.533   $206.53   $206.55   $206.50  
  Purchase #4 $125.62   7.547%   $135.1005   $135.10   $135.10   $135.10  
  Purchase #5 $246.56   8.775%   $268.1956   $268.20   $268.20   $268.20  
  Purchase #6 $245.90   5.224%   $258.7458   $258.75   $258.75   $258.70  
  Purchase #7 $240.59   9.318%   $263.0082   $263.01   $263.00   $263.00  
  7 purchase totals = $1,393.16       $1,514.4111   $1,514.41   $1,514.40   $1,514.30