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 $59.96   3.778%   $62.2253   $62.23   $62.25   $62.20  
  Purchase #2 $183.68   3.249%   $189.6478   $189.65   $189.65   $189.60  
  Purchase #3 $219.99   7.649%   $236.817   $236.82   $236.80   $236.80  
  Purchase #4 $155.89   7.345%   $167.3401   $167.34   $167.35   $167.30  
  Purchase #5 $115.60   7.840%   $124.663   $124.66   $124.65   $124.70  
  Purchase #6 $219.81   5.644%   $232.2161   $232.22   $232.20   $232.20  
  Purchase #7 $184.91   8.283%   $200.2261   $200.23   $200.25   $200.20  
  7 purchase totals = $1,139.84       $1,213.1354   $1,213.15   $1,213.15   $1,213.00