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 $203.61   10.463%   $224.9137   $224.91   $224.90   $224.90  
  Purchase #2 $88.55   13.157%   $100.2005   $100.20   $100.20   $100.20  
  Purchase #3 $64.28   5.274%   $67.6701   $67.67   $67.65   $67.70  
  Purchase #4 $126.91   3.412%   $131.2402   $131.24   $131.25   $131.20  
  Purchase #5 $243.67   11.361%   $271.3533   $271.35   $271.35   $271.40  
  Purchase #6 $173.85   4.596%   $181.8401   $181.84   $181.85   $181.80  
  Purchase #7 $89.60   8.425%   $97.1488   $97.15   $97.15   $97.10  
  7 purchase totals = $990.47       $1,074.3667   $1,074.36   $1,074.35   $1,074.30