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 $53.41   10.529%   $59.0335   $59.03   $59.05   $59.00  
  Purchase #2 $128.46   6.110%   $136.3089   $136.31   $136.30   $136.30  
  Purchase #3 $180.77   9.797%   $198.48   $198.48   $198.50   $198.50  
  Purchase #4 $184.27   9.579%   $201.9212   $201.92   $201.90   $201.90  
  Purchase #5 $192.89   9.136%   $210.5124   $210.51   $210.50   $210.50  
  Purchase #6 $24.93   5.611%   $26.3288   $26.33   $26.35   $26.30  
  Purchase #7 $93.29   12.587%   $105.0324   $105.03   $105.05   $105.00  
  7 purchase totals = $858.02       $937.6172   $937.61   $937.65   $937.50