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 $86.82   7.525%   $93.3532   $93.35   $93.35   $93.40  
  Purchase #2 $190.84   6.281%   $202.8267   $202.83   $202.85   $202.80  
  Purchase #3 $224.52   7.597%   $241.5768   $241.58   $241.60   $241.60  
  Purchase #4 $205.48   9.164%   $224.3102   $224.31   $224.30   $224.30  
  Purchase #5 $84.70   9.183%   $92.478   $92.48   $92.50   $92.50  
  Purchase #6 $164.54   8.739%   $178.9192   $178.92   $178.90   $178.90  
  Purchase #7 $80.96   10.117%   $89.1507   $89.15   $89.15   $89.20  
  7 purchase totals = $1,037.86       $1,122.6148   $1,122.62   $1,122.65   $1,122.70