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 $246.97   7.241%   $264.8531   $264.85   $264.85   $264.90  
  Purchase #2 $177.29   6.179%   $188.2447   $188.24   $188.25   $188.20  
  Purchase #3 $245.36   11.822%   $274.3665   $274.37   $274.35   $274.40  
  Purchase #4 $109.45   12.348%   $122.9649   $122.96   $122.95   $123.00  
  Purchase #5 $80.72   8.213%   $87.3495   $87.35   $87.35   $87.30  
  Purchase #6 $29.26   8.314%   $31.6927   $31.69   $31.70   $31.70  
  Purchase #7 $71.93   4.865%   $75.4294   $75.43   $75.45   $75.40  
  7 purchase totals = $960.98       $1,044.9008   $1,044.89   $1,044.90   $1,044.90