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 $199.60   11.841%   $223.2346   $223.23   $223.25   $223.20  
  Purchase #2 $165.77   12.465%   $186.4332   $186.43   $186.45   $186.40  
  Purchase #3 $226.73   9.273%   $247.7547   $247.75   $247.75   $247.80  
  Purchase #4 $111.63   5.470%   $117.7362   $117.74   $117.75   $117.70  
  Purchase #5 $53.35   11.798%   $59.6442   $59.64   $59.65   $59.60  
  Purchase #6 $148.71   6.347%   $158.1486   $158.15   $158.15   $158.10  
  Purchase #7 $207.52   5.785%   $219.525   $219.53   $219.55   $219.50  
  7 purchase totals = $1,113.31       $1,212.4765   $1,212.47   $1,212.55   $1,212.30