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 $123.37   3.573%   $127.778   $127.78   $127.80   $127.80  
  Purchase #2 $200.44   12.632%   $225.7596   $225.76   $225.75   $225.80  
  Purchase #3 $220.61   11.131%   $245.1661   $245.17   $245.15   $245.20  
  Purchase #4 $121.69   9.185%   $132.8672   $132.87   $132.85   $132.90  
  Purchase #5 $92.72   3.188%   $95.6759   $95.68   $95.70   $95.70  
  Purchase #6 $55.33   9.782%   $60.7424   $60.74   $60.75   $60.70  
  Purchase #7 $184.78   4.397%   $192.9048   $192.90   $192.90   $192.90  
  7 purchase totals = $998.94       $1,080.8940   $1,080.90   $1,080.90   $1,081.00