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 $85.25   10.633%   $94.3146   $94.31   $94.30   $94.30  
  Purchase #2 $203.31   4.251%   $211.9527   $211.95   $211.95   $212.00  
  Purchase #3 $241.80   10.221%   $266.5144   $266.51   $266.50   $266.50  
  Purchase #4 $85.52   9.606%   $93.7351   $93.74   $93.75   $93.70  
  Purchase #5 $24.97   6.402%   $26.5686   $26.57   $26.55   $26.60  
  Purchase #6 $218.37   10.136%   $240.504   $240.50   $240.50   $240.50  
  Purchase #7 $86.46   13.140%   $97.8208   $97.82   $97.80   $97.80  
  7 purchase totals = $945.68       $1,031.4102   $1,031.40   $1,031.35   $1,031.40