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 $229.86   5.212%   $241.8403   $241.84   $241.85   $241.80  
  Purchase #2 $25.51   9.249%   $27.8694   $27.87   $27.85   $27.90  
  Purchase #3 $96.85   11.461%   $107.95   $107.95   $107.95   $108.00  
  Purchase #4 $206.79   3.391%   $213.8022   $213.80   $213.80   $213.80  
  Purchase #5 $120.36   12.163%   $134.9994   $135.00   $135.00   $135.00  
  Purchase #6 $128.94   6.598%   $137.4475   $137.45   $137.45   $137.40  
  Purchase #7 $71.33   9.197%   $77.8902   $77.89   $77.90   $77.90  
  7 purchase totals = $879.64       $941.7990   $941.80   $941.80   $941.80