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 $58.80   11.123%   $65.3403   $65.34   $65.35   $65.30  
  Purchase #2 $225.36   13.310%   $255.3554   $255.36   $255.35   $255.40  
  Purchase #3 $243.56   4.143%   $253.6507   $253.65   $253.65   $253.70  
  Purchase #4 $116.70   3.349%   $120.6083   $120.61   $120.60   $120.60  
  Purchase #5 $43.54   10.381%   $48.0599   $48.06   $48.05   $48.10  
  Purchase #6 $7.27   5.309%   $7.656   $7.66   $7.65   $7.70  
  Purchase #7 $159.52   4.152%   $166.1433   $166.14   $166.15   $166.10  
  7 purchase totals = $854.75       $916.8139   $916.82   $916.80   $916.90