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 $70.95   5.226%   $74.6578   $74.66   $74.65   $74.70  
  Purchase #2 $107.36   8.167%   $116.1281   $116.13   $116.15   $116.10  
  Purchase #3 $158.40   4.373%   $165.3268   $165.33   $165.35   $165.30  
  Purchase #4 $171.67   7.157%   $183.9564   $183.96   $183.95   $184.00  
  Purchase #5 $122.29   12.156%   $137.1556   $137.16   $137.15   $137.20  
  Purchase #6 $174.56   10.198%   $192.3616   $192.36   $192.35   $192.40  
  Purchase #7 $69.74   4.818%   $73.1001   $73.10   $73.10   $73.10  
  7 purchase totals = $874.97       $942.6864   $942.70   $942.70   $942.80