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 $181.98   11.165%   $202.2981   $202.30   $202.30   $202.30  
  Purchase #2 $232.66   10.311%   $256.6496   $256.65   $256.65   $256.60  
  Purchase #3 $234.91   8.578%   $255.0606   $255.06   $255.05   $255.10  
  Purchase #4 $51.60   7.637%   $55.5407   $55.54   $55.55   $55.50  
  Purchase #5 $210.51   9.111%   $229.6896   $229.69   $229.70   $229.70  
  Purchase #6 $192.80   7.280%   $206.8358   $206.84   $206.85   $206.80  
  Purchase #7 $59.98   11.288%   $66.7505   $66.75   $66.75   $66.80  
  7 purchase totals = $1,164.44       $1,272.8249   $1,272.83   $1,272.85   $1,272.80