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 $212.64   3.137%   $219.3105   $219.31   $219.30   $219.30  
  Purchase #2 $69.37   3.725%   $71.954   $71.95   $71.95   $72.00  
  Purchase #3 $47.34   3.326%   $48.9145   $48.91   $48.90   $48.90  
  Purchase #4 $160.56   4.833%   $168.3199   $168.32   $168.30   $168.30  
  Purchase #5 $146.30   7.534%   $157.3222   $157.32   $157.30   $157.30  
  Purchase #6 $141.74   5.132%   $149.0141   $149.01   $149.00   $149.00  
  Purchase #7 $79.52   4.292%   $82.933   $82.93   $82.95   $82.90  
  7 purchase totals = $857.47       $897.7682   $897.75   $897.70   $897.70