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 $46.69   6.619%   $49.7804   $49.78   $49.80   $49.80  
  Purchase #2 $147.34   8.409%   $159.7298   $159.73   $159.75   $159.70  
  Purchase #3 $219.64   12.376%   $246.8226   $246.82   $246.80   $246.80  
  Purchase #4 $25.60   12.144%   $28.7089   $28.71   $28.70   $28.70  
  Purchase #5 $122.85   3.487%   $127.1338   $127.13   $127.15   $127.10  
  Purchase #6 $219.84   11.492%   $245.104   $245.10   $245.10   $245.10  
  Purchase #7 $22.77   4.405%   $23.773   $23.77   $23.75   $23.80  
  7 purchase totals = $804.73       $881.0525   $881.04   $881.05   $881.00