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 $167.82   11.246%   $186.693   $186.69   $186.70   $186.70  
  Purchase #2 $22.89   6.277%   $24.3268   $24.33   $24.35   $24.30  
  Purchase #3 $105.77   4.521%   $110.5519   $110.55   $110.55   $110.60  
  Purchase #4 $161.31   3.811%   $167.4575   $167.46   $167.45   $167.50  
  Purchase #5 $28.96   8.328%   $31.3718   $31.37   $31.35   $31.40  
  Purchase #6 $86.86   8.220%   $93.9999   $94.00   $94.00   $94.00  
  Purchase #7 $169.58   13.137%   $191.8577   $191.86   $191.85   $191.90  
  7 purchase totals = $743.19       $806.2586   $806.26   $806.25   $806.40