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 $187.28   8.652%   $203.4835   $203.48   $203.50   $203.50  
  Purchase #2 $41.43   7.750%   $44.6408   $44.64   $44.65   $44.60  
  Purchase #3 $214.57   8.127%   $232.0081   $232.01   $232.00   $232.00  
  Purchase #4 $169.27   6.614%   $180.4655   $180.47   $180.45   $180.50  
  Purchase #5 $52.52   5.210%   $55.2563   $55.26   $55.25   $55.30  
  Purchase #6 $55.34   5.253%   $58.247   $58.25   $58.25   $58.20  
  Purchase #7 $232.95   13.441%   $264.2608   $264.26   $264.25   $264.30  
  7 purchase totals = $953.36       $1,038.3620   $1,038.37   $1,038.35   $1,038.40