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 $202.43   12.117%   $226.9584   $226.96   $226.95   $227.00  
  Purchase #2 $177.93   7.804%   $191.8157   $191.82   $191.80   $191.80  
  Purchase #3 $65.98   9.663%   $72.3556   $72.36   $72.35   $72.40  
  Purchase #4 $59.73   6.724%   $63.7462   $63.75   $63.75   $63.70  
  Purchase #5 $241.46   9.549%   $264.517   $264.52   $264.50   $264.50  
  Purchase #6 $197.96   10.474%   $218.6943   $218.69   $218.70   $218.70  
  Purchase #7 $109.56   5.476%   $115.5595   $115.56   $115.55   $115.60  
  7 purchase totals = $1,055.05       $1,153.6467   $1,153.66   $1,153.60   $1,153.70