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 $211.44   11.743%   $236.2694   $236.27   $236.25   $236.30  
  Purchase #2 $210.25   5.289%   $221.3701   $221.37   $221.35   $221.40  
  Purchase #3 $130.93   4.179%   $136.4016   $136.40   $136.40   $136.40  
  Purchase #4 $191.29   6.825%   $204.3455   $204.35   $204.35   $204.30  
  Purchase #5 $57.61   3.756%   $59.7738   $59.77   $59.75   $59.80  
  Purchase #6 $69.56   10.280%   $76.7108   $76.71   $76.70   $76.70  
  Purchase #7 $123.30   9.843%   $135.4364   $135.44   $135.45   $135.40  
  7 purchase totals = $994.38       $1,070.3076   $1,070.31   $1,070.25   $1,070.30