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 $59.35   6.134%   $62.9905   $62.99   $63.00   $63.00  
  Purchase #2 $164.77   13.712%   $187.3633   $187.36   $187.35   $187.40  
  Purchase #3 $176.65   12.781%   $199.2276   $199.23   $199.25   $199.20  
  Purchase #4 $206.79   6.347%   $219.915   $219.92   $219.90   $219.90  
  Purchase #5 $184.70   3.527%   $191.2144   $191.21   $191.20   $191.20  
  Purchase #6 $237.94   13.104%   $269.1197   $269.12   $269.10   $269.10  
  Purchase #7 $131.82   12.418%   $148.1894   $148.19   $148.20   $148.20  
  7 purchase totals = $1,162.02       $1,278.0199   $1,278.02   $1,278.00   $1,278.00