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 $91.43   11.572%   $102.0103   $102.01   $102.00   $102.00  
  Purchase #2 $64.93   9.542%   $71.1256   $71.13   $71.15   $71.10  
  Purchase #3 $139.33   12.399%   $156.6055   $156.61   $156.60   $156.60  
  Purchase #4 $45.93   3.594%   $47.5807   $47.58   $47.60   $47.60  
  Purchase #5 $218.60   9.474%   $239.3102   $239.31   $239.30   $239.30  
  Purchase #6 $140.85   4.643%   $147.3897   $147.39   $147.40   $147.40  
  Purchase #7 $174.47   9.505%   $191.0534   $191.05   $191.05   $191.10  
  7 purchase totals = $875.54       $955.0754   $955.08   $955.10   $955.10