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 $70.91   9.326%   $77.5231   $77.52   $77.50   $77.50  
  Purchase #2 $118.91   13.701%   $135.2019   $135.20   $135.20   $135.20  
  Purchase #3 $204.48   11.350%   $227.6885   $227.69   $227.70   $227.70  
  Purchase #4 $153.32   5.239%   $161.3524   $161.35   $161.35   $161.40  
  Purchase #5 $157.32   7.822%   $169.6256   $169.63   $169.65   $169.60  
  Purchase #6 $126.80   12.119%   $142.1669   $142.17   $142.15   $142.20  
  Purchase #7 $106.56   13.347%   $120.7826   $120.78   $120.80   $120.80  
  7 purchase totals = $938.30       $1,034.3410   $1,034.34   $1,034.35   $1,034.40