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 $53.32   6.348%   $56.7048   $56.70   $56.70   $56.70  
  Purchase #2 $189.51   4.779%   $198.5667   $198.57   $198.55   $198.60  
  Purchase #3 $158.98   5.108%   $167.1007   $167.10   $167.10   $167.10  
  Purchase #4 $21.86   6.632%   $23.3098   $23.31   $23.30   $23.30  
  Purchase #5 $182.52   12.674%   $205.6526   $205.65   $205.65   $205.70  
  Purchase #6 $236.69   10.635%   $261.862   $261.86   $261.85   $261.90  
  Purchase #7 $202.82   11.331%   $225.8015   $225.80   $225.80   $225.80  
  7 purchase totals = $1,045.70       $1,138.9981   $1,138.99   $1,138.95   $1,139.10