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 $203.78   11.412%   $227.0354   $227.04   $227.05   $227.00  
  Purchase #2 $188.77   3.222%   $194.8522   $194.85   $194.85   $194.90  
  Purchase #3 $156.31   8.541%   $169.6604   $169.66   $169.65   $169.70  
  Purchase #4 $96.47   4.799%   $101.0996   $101.10   $101.10   $101.10  
  Purchase #5 $128.98   9.471%   $141.1957   $141.20   $141.20   $141.20  
  Purchase #6 $22.70   11.510%   $25.3128   $25.31   $25.30   $25.30  
  Purchase #7 $79.65   11.396%   $88.7269   $88.73   $88.75   $88.70  
  7 purchase totals = $876.66       $947.8830   $947.89   $947.90   $947.90