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 $233.69   12.240%   $262.2937   $262.29   $262.30   $262.30  
  Purchase #2 $127.72   6.367%   $135.8519   $135.85   $135.85   $135.90  
  Purchase #3 $16.28   5.370%   $17.1542   $17.15   $17.15   $17.20  
  Purchase #4 $66.96   10.147%   $73.7544   $73.75   $73.75   $73.80  
  Purchase #5 $165.59   9.374%   $181.1124   $181.11   $181.10   $181.10  
  Purchase #6 $136.48   3.553%   $141.3291   $141.33   $141.35   $141.30  
  Purchase #7 $154.87   6.353%   $164.7089   $164.71   $164.70   $164.70  
  7 purchase totals = $901.59       $976.2046   $976.19   $976.20   $976.30