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 $40.83   6.614%   $43.5305   $43.53   $43.55   $43.50  
  Purchase #2 $76.59   6.586%   $81.6342   $81.63   $81.65   $81.60  
  Purchase #3 $179.61   12.319%   $201.7362   $201.74   $201.75   $201.70  
  Purchase #4 $205.78   9.533%   $225.397   $225.40   $225.40   $225.40  
  Purchase #5 $134.67   5.803%   $142.4849   $142.48   $142.50   $142.50  
  Purchase #6 $51.47   3.112%   $53.0717   $53.07   $53.05   $53.10  
  Purchase #7 $243.30   4.263%   $253.6719   $253.67   $253.65   $253.70  
  7 purchase totals = $932.25       $1,001.5264   $1,001.52   $1,001.55   $1,001.50