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 $7.46   7.859%   $8.0463   $8.05   $8.05   $8.00  
  Purchase #2 $156.46   12.140%   $175.4542   $175.45   $175.45   $175.50  
  Purchase #3 $108.89   3.469%   $112.6674   $112.67   $112.65   $112.70  
  Purchase #4 $200.91   12.667%   $226.3593   $226.36   $226.35   $226.40  
  Purchase #5 $211.68   4.813%   $221.8682   $221.87   $221.85   $221.90  
  Purchase #6 $224.33   8.819%   $244.1137   $244.11   $244.10   $244.10  
  Purchase #7 $69.27   8.116%   $74.892   $74.89   $74.90   $74.90  
  7 purchase totals = $979.00       $1,063.4011   $1,063.40   $1,063.35   $1,063.50