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 $120.70   5.529%   $127.3735   $127.37   $127.35   $127.40  
  Purchase #2 $190.30   10.784%   $210.822   $210.82   $210.80   $210.80  
  Purchase #3 $149.70   10.538%   $165.4754   $165.48   $165.50   $165.50  
  Purchase #4 $30.43   5.857%   $32.2123   $32.21   $32.20   $32.20  
  Purchase #5 $70.54   13.660%   $80.1758   $80.18   $80.20   $80.20  
  Purchase #6 $45.81   6.850%   $48.948   $48.95   $48.95   $48.90  
  Purchase #7 $38.62   6.643%   $41.1855   $41.19   $41.20   $41.20  
  7 purchase totals = $646.10       $706.1925   $706.20   $706.20   $706.20