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 $75.60   13.454%   $85.7712   $85.77   $85.75   $85.80  
  Purchase #2 $174.46   9.827%   $191.6042   $191.60   $191.60   $191.60  
  Purchase #3 $26.81   5.339%   $28.2414   $28.24   $28.25   $28.20  
  Purchase #4 $236.48   4.603%   $247.3652   $247.37   $247.35   $247.40  
  Purchase #5 $221.98   4.513%   $231.998   $232.00   $232.00   $232.00  
  Purchase #6 $123.88   4.579%   $129.5525   $129.55   $129.55   $129.60  
  Purchase #7 $106.40   9.413%   $116.4154   $116.42   $116.40   $116.40  
  7 purchase totals = $965.61       $1,030.9479   $1,030.95   $1,030.90   $1,031.00