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 $193.46   4.446%   $202.0612   $202.06   $202.05   $202.10  
  Purchase #2 $32.62   13.244%   $36.9402   $36.94   $36.95   $36.90  
  Purchase #3 $105.51   11.292%   $117.4242   $117.42   $117.40   $117.40  
  Purchase #4 $119.73   6.837%   $127.9159   $127.92   $127.90   $127.90  
  Purchase #5 $62.68   6.824%   $66.9573   $66.96   $66.95   $67.00  
  Purchase #6 $180.42   9.482%   $197.5274   $197.53   $197.55   $197.50  
  Purchase #7 $7.56   11.415%   $8.423   $8.42   $8.40   $8.40  
  7 purchase totals = $701.98       $757.2492   $757.25   $757.20   $757.20