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 $212.26   9.712%   $232.8747   $232.87   $232.85   $232.90  
  Purchase #2 $199.63   5.582%   $210.7733   $210.77   $210.75   $210.80  
  Purchase #3 $150.35   3.211%   $155.1777   $155.18   $155.20   $155.20  
  Purchase #4 $122.26   9.479%   $133.849   $133.85   $133.85   $133.80  
  Purchase #5 $158.52   11.708%   $177.0795   $177.08   $177.10   $177.10  
  Purchase #6 $59.47   10.379%   $65.6424   $65.64   $65.65   $65.60  
  Purchase #7 $28.68   5.626%   $30.2935   $30.29   $30.30   $30.30  
  7 purchase totals = $931.17       $1,005.6901   $1,005.68   $1,005.70   $1,005.70