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 $154.42   12.114%   $173.1264   $173.13   $173.15   $173.10  
  Purchase #2 $54.93   7.165%   $58.8657   $58.87   $58.85   $58.90  
  Purchase #3 $54.56   12.751%   $61.5169   $61.52   $61.50   $61.50  
  Purchase #4 $146.34   10.232%   $161.3135   $161.31   $161.30   $161.30  
  Purchase #5 $178.55   12.228%   $200.3831   $200.38   $200.40   $200.40  
  Purchase #6 $166.37   3.202%   $171.6972   $171.70   $171.70   $171.70  
  Purchase #7 $214.41   4.494%   $224.0456   $224.05   $224.05   $224.00  
  7 purchase totals = $969.58       $1,050.9484   $1,050.96   $1,050.95   $1,050.90