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 $234.86   13.839%   $267.3623   $267.36   $267.35   $267.40  
  Purchase #2 $164.94   9.358%   $180.3751   $180.38   $180.40   $180.40  
  Purchase #3 $48.79   12.132%   $54.7092   $54.71   $54.70   $54.70  
  Purchase #4 $97.62   3.384%   $100.9235   $100.92   $100.90   $100.90  
  Purchase #5 $219.43   3.136%   $226.3113   $226.31   $226.30   $226.30  
  Purchase #6 $148.28   12.603%   $166.9677   $166.97   $166.95   $167.00  
  Purchase #7 $57.43   8.399%   $62.2535   $62.25   $62.25   $62.30  
  7 purchase totals = $971.35       $1,058.9026   $1,058.90   $1,058.85   $1,059.00