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 $168.62   10.472%   $186.2779   $186.28   $186.30   $186.30  
  Purchase #2 $70.90   6.113%   $75.2341   $75.23   $75.25   $75.20  
  Purchase #3 $55.95   10.741%   $61.9596   $61.96   $61.95   $62.00  
  Purchase #4 $123.47   6.631%   $131.6573   $131.66   $131.65   $131.70  
  Purchase #5 $19.85   10.174%   $21.8695   $21.87   $21.85   $21.90  
  Purchase #6 $210.96   10.170%   $232.4146   $232.41   $232.40   $232.40  
  Purchase #7 $147.31   12.373%   $165.5367   $165.54   $165.55   $165.50  
  7 purchase totals = $797.06       $874.9497   $874.95   $874.95   $875.00