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 $212.62   3.827%   $220.757   $220.76   $220.75   $220.80  
  Purchase #2 $80.78   8.164%   $87.3749   $87.37   $87.35   $87.40  
  Purchase #3 $42.65   4.537%   $44.585   $44.59   $44.60   $44.60  
  Purchase #4 $171.73   5.615%   $181.3726   $181.37   $181.35   $181.40  
  Purchase #5 $67.53   9.415%   $73.8879   $73.89   $73.90   $73.90  
  Purchase #6 $185.60   13.240%   $210.1734   $210.17   $210.15   $210.20  
  Purchase #7 $206.28   13.559%   $234.2495   $234.25   $234.25   $234.20  
  7 purchase totals = $967.19       $1,052.4003   $1,052.40   $1,052.35   $1,052.50