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 $95.29   9.420%   $104.2663   $104.27   $104.25   $104.30  
  Purchase #2 $242.86   11.325%   $270.3639   $270.36   $270.35   $270.40  
  Purchase #3 $64.27   5.706%   $67.9372   $67.94   $67.95   $67.90  
  Purchase #4 $59.51   6.763%   $63.5347   $63.53   $63.55   $63.50  
  Purchase #5 $232.64   5.747%   $246.0098   $246.01   $246.00   $246.00  
  Purchase #6 $135.72   9.771%   $148.9812   $148.98   $149.00   $149.00  
  Purchase #7 $129.52   4.586%   $135.4598   $135.46   $135.45   $135.50  
  7 purchase totals = $959.81       $1,036.5529   $1,036.55   $1,036.55   $1,036.60