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 $59.43   9.647%   $65.1632   $65.16   $65.15   $65.20  
  Purchase #2 $23.54   10.483%   $26.0077   $26.01   $26.00   $26.00  
  Purchase #3 $214.29   10.527%   $236.8483   $236.85   $236.85   $236.80  
  Purchase #4 $110.75   12.871%   $125.0046   $125.00   $125.00   $125.00  
  Purchase #5 $247.25   6.864%   $264.2212   $264.22   $264.20   $264.20  
  Purchase #6 $132.31   6.145%   $140.4404   $140.44   $140.45   $140.40  
  Purchase #7 $134.31   12.309%   $150.8422   $150.84   $150.85   $150.80  
  7 purchase totals = $921.88       $1,008.5276   $1,008.52   $1,008.50   $1,008.40