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 $136.63   3.784%   $141.8001   $141.80   $141.80   $141.80  
  Purchase #2 $238.65   13.114%   $269.9466   $269.95   $269.95   $269.90  
  Purchase #3 $156.65   3.216%   $161.6879   $161.69   $161.70   $161.70  
  Purchase #4 $62.60   9.662%   $68.6484   $68.65   $68.65   $68.60  
  Purchase #5 $13.80   12.363%   $15.5061   $15.51   $15.50   $15.50  
  Purchase #6 $228.51   6.571%   $243.5254   $243.53   $243.55   $243.50  
  Purchase #7 $209.92   8.137%   $227.0012   $227.00   $227.00   $227.00  
  7 purchase totals = $1,046.76       $1,128.1157   $1,128.13   $1,128.15   $1,128.00