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 $135.76   9.784%   $149.0428   $149.04   $149.05   $149.00  
  Purchase #2 $187.71   7.803%   $202.357   $202.36   $202.35   $202.40  
  Purchase #3 $243.52   6.658%   $259.7336   $259.73   $259.75   $259.70  
  Purchase #4 $113.96   7.837%   $122.891   $122.89   $122.90   $122.90  
  Purchase #5 $164.96   4.789%   $172.8599   $172.86   $172.85   $172.90  
  Purchase #6 $213.86   3.601%   $221.5611   $221.56   $221.55   $221.60  
  Purchase #7 $71.54   5.468%   $75.4518   $75.45   $75.45   $75.50  
  7 purchase totals = $1,131.31       $1,203.8972   $1,203.89   $1,203.90   $1,204.00