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 $189.84   11.133%   $210.9749   $210.97   $210.95   $211.00  
  Purchase #2 $43.49   7.624%   $46.8057   $46.81   $46.80   $46.80  
  Purchase #3 $116.51   11.294%   $129.6686   $129.67   $129.65   $129.70  
  Purchase #4 $247.28   3.143%   $255.052   $255.05   $255.05   $255.10  
  Purchase #5 $118.41   5.240%   $124.6147   $124.61   $124.60   $124.60  
  Purchase #6 $161.85   8.163%   $175.0618   $175.06   $175.05   $175.10  
  Purchase #7 $232.71   5.293%   $245.0273   $245.03   $245.05   $245.00  
  7 purchase totals = $1,110.09       $1,187.2050   $1,187.20   $1,187.15   $1,187.30