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 $92.99   5.763%   $98.349   $98.35   $98.35   $98.30  
  Purchase #2 $33.78   11.457%   $37.6502   $37.65   $37.65   $37.70  
  Purchase #3 $6.49   4.363%   $6.7732   $6.77   $6.75   $6.80  
  Purchase #4 $104.99   3.180%   $108.3287   $108.33   $108.35   $108.30  
  Purchase #5 $116.86   13.463%   $132.5929   $132.59   $132.60   $132.60  
  Purchase #6 $192.93   7.247%   $206.9116   $206.91   $206.90   $206.90  
  Purchase #7 $92.91   12.860%   $104.8582   $104.86   $104.85   $104.90  
  7 purchase totals = $640.95       $695.4638   $695.46   $695.45   $695.50