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 $225.85   9.244%   $246.7276   $246.73   $246.75   $246.70  
  Purchase #2 $223.34   4.623%   $233.665   $233.67   $233.65   $233.70  
  Purchase #3 $126.95   7.639%   $136.6477   $136.65   $136.65   $136.60  
  Purchase #4 $63.31   4.722%   $66.2995   $66.30   $66.30   $66.30  
  Purchase #5 $215.97   13.461%   $245.0417   $245.04   $245.05   $245.00  
  Purchase #6 $244.56   10.153%   $269.3902   $269.39   $269.40   $269.40  
  Purchase #7 $157.59   5.759%   $166.6656   $166.67   $166.65   $166.70  
  7 purchase totals = $1,257.57       $1,364.4373   $1,364.45   $1,364.45   $1,364.40