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 $81.45   5.374%   $85.8271   $85.83   $85.85   $85.80  
  Purchase #2 $230.98   7.649%   $248.6477   $248.65   $248.65   $248.60  
  Purchase #3 $189.94   5.157%   $199.7352   $199.74   $199.75   $199.70  
  Purchase #4 $164.94   11.171%   $183.3654   $183.37   $183.35   $183.40  
  Purchase #5 $17.61   6.140%   $18.6913   $18.69   $18.70   $18.70  
  Purchase #6 $44.62   8.290%   $48.319   $48.32   $48.30   $48.30  
  Purchase #7 $181.68   10.736%   $201.1852   $201.19   $201.20   $201.20  
  7 purchase totals = $911.22       $985.7709   $985.79   $985.80   $985.70