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 $61.82   13.506%   $70.1694   $70.17   $70.15   $70.20  
  Purchase #2 $84.27   8.424%   $91.3689   $91.37   $91.35   $91.40  
  Purchase #3 $95.80   13.250%   $108.4935   $108.49   $108.50   $108.50  
  Purchase #4 $158.70   6.873%   $169.6075   $169.61   $169.60   $169.60  
  Purchase #5 $26.70   5.427%   $28.149   $28.15   $28.15   $28.10  
  Purchase #6 $122.70   5.104%   $128.9626   $128.96   $128.95   $129.00  
  Purchase #7 $148.81   12.631%   $167.6062   $167.61   $167.60   $167.60  
  7 purchase totals = $698.80       $764.3571   $764.36   $764.30   $764.40