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 $117.98   12.763%   $133.0378   $133.04   $133.05   $133.00  
  Purchase #2 $90.40   10.359%   $99.7645   $99.76   $99.75   $99.80  
  Purchase #3 $180.33   10.182%   $198.6912   $198.69   $198.70   $198.70  
  Purchase #4 $181.77   3.250%   $187.6775   $187.68   $187.70   $187.70  
  Purchase #5 $216.69   4.700%   $226.8744   $226.87   $226.85   $226.90  
  Purchase #6 $142.90   3.237%   $147.5257   $147.53   $147.55   $147.50  
  Purchase #7 $22.69   12.828%   $25.6007   $25.60   $25.60   $25.60  
  7 purchase totals = $952.76       $1,019.1718   $1,019.17   $1,019.20   $1,019.20