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 $88.61   6.665%   $94.5159   $94.52   $94.50   $94.50  
  Purchase #2 $241.53   11.668%   $269.7117   $269.71   $269.70   $269.70  
  Purchase #3 $36.28   10.380%   $40.0459   $40.05   $40.05   $40.00  
  Purchase #4 $163.41   13.126%   $184.8592   $184.86   $184.85   $184.90  
  Purchase #5 $244.79   12.311%   $274.9261   $274.93   $274.95   $274.90  
  Purchase #6 $206.52   11.774%   $230.8357   $230.84   $230.85   $230.80  
  Purchase #7 $242.62   5.449%   $255.8404   $255.84   $255.85   $255.80  
  7 purchase totals = $1,223.76       $1,350.7349   $1,350.75   $1,350.75   $1,350.60