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 $58.98   7.374%   $63.3292   $63.33   $63.35   $63.30  
  Purchase #2 $108.63   9.276%   $118.7065   $118.71   $118.70   $118.70  
  Purchase #3 $25.89   6.277%   $27.5151   $27.52   $27.50   $27.50  
  Purchase #4 $157.37   4.121%   $163.8552   $163.86   $163.85   $163.90  
  Purchase #5 $31.45   10.690%   $34.812   $34.81   $34.80   $34.80  
  Purchase #6 $128.46   10.588%   $142.0613   $142.06   $142.05   $142.10  
  Purchase #7 $183.63   7.584%   $197.5565   $197.56   $197.55   $197.60  
  7 purchase totals = $694.41       $747.8358   $747.85   $747.80   $747.90