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 $86.42   9.627%   $94.7397   $94.74   $94.75   $94.70  
  Purchase #2 $235.79   10.543%   $260.6493   $260.65   $260.65   $260.60  
  Purchase #3 $107.78   13.363%   $122.1826   $122.18   $122.20   $122.20  
  Purchase #4 $209.34   4.730%   $219.2418   $219.24   $219.25   $219.20  
  Purchase #5 $108.55   6.320%   $115.4104   $115.41   $115.40   $115.40  
  Purchase #6 $225.35   12.847%   $254.3007   $254.30   $254.30   $254.30  
  Purchase #7 $201.89   5.396%   $212.784   $212.78   $212.80   $212.80  
  7 purchase totals = $1,175.12       $1,279.3085   $1,279.30   $1,279.35   $1,279.20