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 $69.31   5.660%   $73.2329   $73.23   $73.25   $73.20  
  Purchase #2 $78.69   3.236%   $81.2364   $81.24   $81.25   $81.20  
  Purchase #3 $112.45   3.625%   $116.5263   $116.53   $116.55   $116.50  
  Purchase #4 $11.51   12.146%   $12.908   $12.91   $12.90   $12.90  
  Purchase #5 $178.56   5.392%   $188.188   $188.19   $188.20   $188.20  
  Purchase #6 $142.59   5.398%   $150.287   $150.29   $150.30   $150.30  
  Purchase #7 $209.62   6.392%   $223.0189   $223.02   $223.00   $223.00  
  7 purchase totals = $802.73       $845.3975   $845.41   $845.45   $845.30