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 $226.67   6.855%   $242.2082   $242.21   $242.20   $242.20  
  Purchase #2 $157.28   12.871%   $177.5235   $177.52   $177.50   $177.50  
  Purchase #3 $119.84   13.808%   $136.3875   $136.39   $136.40   $136.40  
  Purchase #4 $211.34   7.416%   $227.013   $227.01   $227.00   $227.00  
  Purchase #5 $124.42   8.665%   $135.201   $135.20   $135.20   $135.20  
  Purchase #6 $38.94   7.689%   $41.9341   $41.93   $41.95   $41.90  
  Purchase #7 $79.53   7.453%   $85.4574   $85.46   $85.45   $85.50  
  7 purchase totals = $958.02       $1,045.7247   $1,045.72   $1,045.70   $1,045.70