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 $246.87   6.743%   $263.5164   $263.52   $263.50   $263.50  
  Purchase #2 $65.41   13.636%   $74.3293   $74.33   $74.35   $74.30  
  Purchase #3 $68.99   9.428%   $75.4944   $75.49   $75.50   $75.50  
  Purchase #4 $37.67   7.305%   $40.4218   $40.42   $40.40   $40.40  
  Purchase #5 $225.36   6.419%   $239.8259   $239.83   $239.85   $239.80  
  Purchase #6 $54.79   5.381%   $57.7382   $57.74   $57.75   $57.70  
  Purchase #7 $153.26   7.677%   $165.0258   $165.03   $165.05   $165.00  
  7 purchase totals = $852.35       $916.3518   $916.36   $916.40   $916.20