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 $226.43   12.212%   $254.0816   $254.08   $254.10   $254.10  
  Purchase #2 $164.58   11.412%   $183.3619   $183.36   $183.35   $183.40  
  Purchase #3 $220.78   12.488%   $248.351   $248.35   $248.35   $248.40  
  Purchase #4 $101.60   10.741%   $112.5129   $112.51   $112.50   $112.50  
  Purchase #5 $95.58   12.633%   $107.6546   $107.65   $107.65   $107.70  
  Purchase #6 $123.48   12.577%   $139.0101   $139.01   $139.00   $139.00  
  Purchase #7 $47.60   5.811%   $50.366   $50.37   $50.35   $50.40  
  7 purchase totals = $980.05       $1,095.3381   $1,095.33   $1,095.30   $1,095.50