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 $186.67   13.179%   $211.2712   $211.27   $211.25   $211.30  
  Purchase #2 $100.94   6.541%   $107.5425   $107.54   $107.55   $107.50  
  Purchase #3 $54.84   7.859%   $59.1499   $59.15   $59.15   $59.10  
  Purchase #4 $62.41   5.187%   $65.6472   $65.65   $65.65   $65.60  
  Purchase #5 $199.30   12.378%   $223.9694   $223.97   $223.95   $224.00  
  Purchase #6 $100.84   11.398%   $112.3337   $112.33   $112.35   $112.30  
  Purchase #7 $249.79   9.202%   $272.7757   $272.78   $272.80   $272.80  
  7 purchase totals = $954.79       $1,052.6896   $1,052.69   $1,052.70   $1,052.60