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 $191.93   8.234%   $207.7335   $207.73   $207.75   $207.70  
  Purchase #2 $36.88   12.555%   $41.5103   $41.51   $41.50   $41.50  
  Purchase #3 $144.99   6.115%   $153.8561   $153.86   $153.85   $153.90  
  Purchase #4 $11.75   7.284%   $12.6059   $12.61   $12.60   $12.60  
  Purchase #5 $152.85   5.438%   $161.162   $161.16   $161.15   $161.20  
  Purchase #6 $101.92   10.839%   $112.9671   $112.97   $112.95   $113.00  
  Purchase #7 $105.93   11.751%   $118.3778   $118.38   $118.40   $118.40  
  7 purchase totals = $746.25       $808.2127   $808.22   $808.20   $808.30