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 $240.97   6.814%   $257.3897   $257.39   $257.40   $257.40  
  Purchase #2 $238.82   11.151%   $265.4508   $265.45   $265.45   $265.50  
  Purchase #3 $91.26   7.557%   $98.1565   $98.16   $98.15   $98.20  
  Purchase #4 $55.56   6.555%   $59.202   $59.20   $59.20   $59.20  
  Purchase #5 $73.68   13.478%   $83.6106   $83.61   $83.60   $83.60  
  Purchase #6 $211.93   6.255%   $225.1862   $225.19   $225.20   $225.20  
  Purchase #7 $16.28   6.511%   $17.34   $17.34   $17.35   $17.30  
  7 purchase totals = $928.50       $1,006.3358   $1,006.34   $1,006.35   $1,006.40