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 $83.56   12.351%   $93.8805   $93.88   $93.90   $93.90  
  Purchase #2 $240.53   13.598%   $273.2373   $273.24   $273.25   $273.20  
  Purchase #3 $249.29   6.386%   $265.2097   $265.21   $265.20   $265.20  
  Purchase #4 $112.81   3.156%   $116.3703   $116.37   $116.35   $116.40  
  Purchase #5 $135.94   13.121%   $153.7767   $153.78   $153.80   $153.80  
  Purchase #6 $39.75   11.833%   $44.4536   $44.45   $44.45   $44.50  
  Purchase #7 $46.90   5.113%   $49.298   $49.30   $49.30   $49.30  
  7 purchase totals = $908.78       $996.2261   $996.23   $996.25   $996.30