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 $8.51   9.651%   $9.3313   $9.33   $9.35   $9.30  
  Purchase #2 $242.97   6.206%   $258.0487   $258.05   $258.05   $258.00  
  Purchase #3 $213.31   11.232%   $237.269   $237.27   $237.25   $237.30  
  Purchase #4 $61.57   5.858%   $65.1768   $65.18   $65.20   $65.20  
  Purchase #5 $164.92   12.585%   $185.6752   $185.68   $185.70   $185.70  
  Purchase #6 $83.39   6.140%   $88.5101   $88.51   $88.50   $88.50  
  Purchase #7 $108.98   11.566%   $121.5846   $121.58   $121.60   $121.60  
  7 purchase totals = $883.65       $965.5957   $965.60   $965.65   $965.60