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 $76.44   10.812%   $84.7047   $84.70   $84.70   $84.70  
  Purchase #2 $51.64   6.167%   $54.8246   $54.82   $54.80   $54.80  
  Purchase #3 $81.46   4.573%   $85.1852   $85.19   $85.20   $85.20  
  Purchase #4 $183.33   8.306%   $198.5574   $198.56   $198.55   $198.60  
  Purchase #5 $146.30   7.700%   $157.5651   $157.57   $157.55   $157.60  
  Purchase #6 $217.51   7.107%   $232.9684   $232.97   $232.95   $233.00  
  Purchase #7 $147.80   4.313%   $154.1746   $154.17   $154.15   $154.20  
  7 purchase totals = $904.48       $967.9800   $967.98   $967.90   $968.10