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 $112.82   9.703%   $123.7669   $123.77   $123.75   $123.80  
  Purchase #2 $193.82   6.282%   $205.9958   $206.00   $206.00   $206.00  
  Purchase #3 $59.28   8.402%   $64.2607   $64.26   $64.25   $64.30  
  Purchase #4 $225.84   7.473%   $242.717   $242.72   $242.70   $242.70  
  Purchase #5 $167.59   10.825%   $185.7316   $185.73   $185.75   $185.70  
  Purchase #6 $34.27   12.728%   $38.6319   $38.63   $38.65   $38.60  
  Purchase #7 $224.31   3.228%   $231.5507   $231.55   $231.55   $231.60  
  7 purchase totals = $1,017.93       $1,092.6546   $1,092.66   $1,092.65   $1,092.70