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 $181.89   11.365%   $202.5618   $202.56   $202.55   $202.60  
  Purchase #2 $198.63   10.328%   $219.1445   $219.14   $219.15   $219.10  
  Purchase #3 $236.56   4.384%   $246.9308   $246.93   $246.95   $246.90  
  Purchase #4 $93.66   11.528%   $104.4571   $104.46   $104.45   $104.50  
  Purchase #5 $124.83   5.245%   $131.3773   $131.38   $131.40   $131.40  
  Purchase #6 $170.98   11.529%   $190.6923   $190.69   $190.70   $190.70  
  Purchase #7 $21.40   12.234%   $24.0181   $24.02   $24.00   $24.00  
  7 purchase totals = $1,027.95       $1,119.1819   $1,119.18   $1,119.20   $1,119.20