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 $86.78   7.830%   $93.5749   $93.57   $93.55   $93.60  
  Purchase #2 $141.83   4.184%   $147.7642   $147.76   $147.75   $147.80  
  Purchase #3 $104.57   13.177%   $118.3492   $118.35   $118.35   $118.30  
  Purchase #4 $66.26   5.132%   $69.6605   $69.66   $69.65   $69.70  
  Purchase #5 $187.53   6.375%   $199.485   $199.49   $199.50   $199.50  
  Purchase #6 $45.33   5.671%   $47.9007   $47.90   $47.90   $47.90  
  Purchase #7 $25.45   11.149%   $28.2874   $28.29   $28.30   $28.30  
  7 purchase totals = $657.75       $705.0219   $705.02   $705.00   $705.10