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 $38.76   5.806%   $41.0104   $41.01   $41.00   $41.00  
  Purchase #2 $237.39   7.415%   $254.9925   $254.99   $255.00   $255.00  
  Purchase #3 $78.28   3.495%   $81.0159   $81.02   $81.00   $81.00  
  Purchase #4 $113.87   8.502%   $123.5512   $123.55   $123.55   $123.60  
  Purchase #5 $98.81   9.821%   $108.5141   $108.51   $108.50   $108.50  
  Purchase #6 $233.27   11.367%   $259.7858   $259.79   $259.80   $259.80  
  Purchase #7 $118.32   6.304%   $125.7789   $125.78   $125.80   $125.80  
  7 purchase totals = $918.70       $994.6488   $994.65   $994.65   $994.70