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 $183.95   10.330%   $202.952   $202.95   $202.95   $203.00  
  Purchase #2 $61.38   13.422%   $69.6184   $69.62   $69.60   $69.60  
  Purchase #3 $58.35   9.845%   $64.0946   $64.09   $64.10   $64.10  
  Purchase #4 $124.59   3.423%   $128.8547   $128.85   $128.85   $128.90  
  Purchase #5 $151.60   13.485%   $172.0433   $172.04   $172.05   $172.00  
  Purchase #6 $103.37   9.414%   $113.1013   $113.10   $113.10   $113.10  
  Purchase #7 $71.52   12.781%   $80.661   $80.66   $80.65   $80.70  
  7 purchase totals = $754.76       $831.3253   $831.31   $831.30   $831.40