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 $224.46   12.162%   $251.7588   $251.76   $251.75   $251.80  
  Purchase #2 $160.57   9.567%   $175.9317   $175.93   $175.95   $175.90  
  Purchase #3 $64.58   12.297%   $72.5214   $72.52   $72.50   $72.50  
  Purchase #4 $36.34   7.129%   $38.9307   $38.93   $38.95   $38.90  
  Purchase #5 $226.89   9.202%   $247.7684   $247.77   $247.75   $247.80  
  Purchase #6 $44.98   6.360%   $47.8407   $47.84   $47.85   $47.80  
  Purchase #7 $199.84   9.790%   $219.4043   $219.40   $219.40   $219.40  
  7 purchase totals = $957.66       $1,054.1560   $1,054.15   $1,054.15   $1,054.10