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 $88.97   5.294%   $93.6801   $93.68   $93.70   $93.70  
  Purchase #2 $72.96   9.231%   $79.6949   $79.69   $79.70   $79.70  
  Purchase #3 $211.46   9.331%   $231.1913   $231.19   $231.20   $231.20  
  Purchase #4 $116.65   8.222%   $126.241   $126.24   $126.25   $126.20  
  Purchase #5 $215.30   5.568%   $227.2879   $227.29   $227.30   $227.30  
  Purchase #6 $43.44   8.223%   $47.0121   $47.01   $47.00   $47.00  
  Purchase #7 $143.91   4.498%   $150.3831   $150.38   $150.40   $150.40  
  7 purchase totals = $892.69       $955.4904   $955.48   $955.55   $955.50