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 $170.92   13.144%   $193.3857   $193.39   $193.40   $193.40  
  Purchase #2 $150.86   9.646%   $165.412   $165.41   $165.40   $165.40  
  Purchase #3 $130.37   4.713%   $136.5143   $136.51   $136.50   $136.50  
  Purchase #4 $77.57   8.605%   $84.2449   $84.24   $84.25   $84.20  
  Purchase #5 $104.84   11.363%   $116.753   $116.75   $116.75   $116.80  
  Purchase #6 $223.86   12.728%   $252.3529   $252.35   $252.35   $252.40  
  Purchase #7 $12.91   8.159%   $13.9633   $13.96   $13.95   $14.00  
  7 purchase totals = $871.33       $962.6261   $962.61   $962.60   $962.70