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 $220.55   11.573%   $246.0743   $246.07   $246.05   $246.10  
  Purchase #2 $249.84   9.214%   $272.8603   $272.86   $272.85   $272.90  
  Purchase #3 $94.97   10.556%   $104.995   $105.00   $105.00   $105.00  
  Purchase #4 $194.64   9.870%   $213.851   $213.85   $213.85   $213.90  
  Purchase #5 $97.70   6.562%   $104.1111   $104.11   $104.10   $104.10  
  Purchase #6 $151.30   13.718%   $172.0553   $172.06   $172.05   $172.10  
  Purchase #7 $22.37   7.831%   $24.1218   $24.12   $24.10   $24.10  
  7 purchase totals = $1,031.37       $1,138.0688   $1,138.07   $1,138.00   $1,138.20