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 $127.91   10.307%   $141.0937   $141.09   $141.10   $141.10  
  Purchase #2 $202.93   8.268%   $219.7083   $219.71   $219.70   $219.70  
  Purchase #3 $123.28   6.317%   $131.0676   $131.07   $131.05   $131.10  
  Purchase #4 $86.95   7.686%   $93.633   $93.63   $93.65   $93.60  
  Purchase #5 $246.56   9.331%   $269.5665   $269.57   $269.55   $269.60  
  Purchase #6 $74.74   7.679%   $80.4793   $80.48   $80.50   $80.50  
  Purchase #7 $5.94   8.791%   $6.4622   $6.46   $6.45   $6.50  
  7 purchase totals = $868.31       $942.0106   $942.01   $942.00   $942.10