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 $46.62   7.667%   $50.1944   $50.19   $50.20   $50.20  
  Purchase #2 $243.50   10.483%   $269.0261   $269.03   $269.05   $269.00  
  Purchase #3 $119.41   4.723%   $125.0497   $125.05   $125.05   $125.00  
  Purchase #4 $206.79   3.455%   $213.9346   $213.93   $213.95   $213.90  
  Purchase #5 $110.98   4.808%   $116.3159   $116.32   $116.30   $116.30  
  Purchase #6 $60.76   11.525%   $67.7626   $67.76   $67.75   $67.80  
  Purchase #7 $210.35   8.831%   $228.926   $228.93   $228.95   $228.90  
  7 purchase totals = $998.41       $1,071.2093   $1,071.21   $1,071.25   $1,071.10