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 $185.62   11.541%   $207.0424   $207.04   $207.05   $207.00  
  Purchase #2 $72.74   4.234%   $75.8198   $75.82   $75.80   $75.80  
  Purchase #3 $98.45   12.645%   $110.899   $110.90   $110.90   $110.90  
  Purchase #4 $36.58   5.259%   $38.5037   $38.50   $38.50   $38.50  
  Purchase #5 $246.66   4.155%   $256.9087   $256.91   $256.90   $256.90  
  Purchase #6 $218.29   11.742%   $243.9216   $243.92   $243.90   $243.90  
  Purchase #7 $140.27   12.417%   $157.6873   $157.69   $157.70   $157.70  
  7 purchase totals = $998.61       $1,090.7825   $1,090.78   $1,090.75   $1,090.70