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 $55.73   11.452%   $62.1122   $62.11   $62.10   $62.10  
  Purchase #2 $140.54   4.676%   $147.1117   $147.11   $147.10   $147.10  
  Purchase #3 $189.64   5.144%   $199.3951   $199.40   $199.40   $199.40  
  Purchase #4 $195.94   11.528%   $218.528   $218.53   $218.55   $218.50  
  Purchase #5 $27.48   6.142%   $29.1678   $29.17   $29.15   $29.20  
  Purchase #6 $129.44   4.821%   $135.6803   $135.68   $135.70   $135.70  
  Purchase #7 $250.41   5.145%   $263.2936   $263.29   $263.30   $263.30  
  7 purchase totals = $989.18       $1,055.2887   $1,055.29   $1,055.30   $1,055.30