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 $212.54   6.272%   $225.8705   $225.87   $225.85   $225.90  
  Purchase #2 $240.72   10.441%   $265.8536   $265.85   $265.85   $265.90  
  Purchase #3 $159.54   11.186%   $177.3861   $177.39   $177.40   $177.40  
  Purchase #4 $145.27   11.154%   $161.4734   $161.47   $161.45   $161.50  
  Purchase #5 $77.69   4.854%   $81.4611   $81.46   $81.45   $81.50  
  Purchase #6 $78.52   5.267%   $82.6556   $82.66   $82.65   $82.70  
  Purchase #7 $162.32   9.221%   $177.2875   $177.29   $177.30   $177.30  
  7 purchase totals = $1,076.60       $1,171.9878   $1,171.99   $1,171.95   $1,172.20