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 $43.46   12.659%   $48.9616   $48.96   $48.95   $49.00  
  Purchase #2 $68.88   4.294%   $71.8377   $71.84   $71.85   $71.80  
  Purchase #3 $68.59   11.528%   $76.4971   $76.50   $76.50   $76.50  
  Purchase #4 $89.42   4.418%   $93.3706   $93.37   $93.35   $93.40  
  Purchase #5 $148.62   6.238%   $157.8909   $157.89   $157.90   $157.90  
  Purchase #6 $226.60   12.135%   $254.0979   $254.10   $254.10   $254.10  
  Purchase #7 $45.52   4.494%   $47.5657   $47.57   $47.55   $47.60  
  7 purchase totals = $691.09       $750.2215   $750.23   $750.20   $750.30