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 $222.72   10.435%   $245.9608   $245.96   $245.95   $246.00  
  Purchase #2 $232.80   5.822%   $246.3536   $246.35   $246.35   $246.40  
  Purchase #3 $158.29   11.822%   $177.003   $177.00   $177.00   $177.00  
  Purchase #4 $217.52   4.561%   $227.4411   $227.44   $227.45   $227.40  
  Purchase #5 $25.48   4.465%   $26.6177   $26.62   $26.60   $26.60  
  Purchase #6 $182.75   11.414%   $203.6091   $203.61   $203.60   $203.60  
  Purchase #7 $130.77   6.146%   $138.8071   $138.81   $138.80   $138.80  
  7 purchase totals = $1,170.33       $1,265.7924   $1,265.79   $1,265.75   $1,265.80