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 $129.49   3.682%   $134.2578   $134.26   $134.25   $134.30  
  Purchase #2 $58.66   3.862%   $60.9254   $60.93   $60.95   $60.90  
  Purchase #3 $156.61   3.561%   $162.1869   $162.19   $162.20   $162.20  
  Purchase #4 $202.40   3.589%   $209.6641   $209.66   $209.65   $209.70  
  Purchase #5 $185.88   9.441%   $203.4289   $203.43   $203.45   $203.40  
  Purchase #6 $247.72   6.418%   $263.6187   $263.62   $263.60   $263.60  
  Purchase #7 $134.39   6.250%   $142.7894   $142.79   $142.80   $142.80  
  7 purchase totals = $1,115.15       $1,176.8712   $1,176.88   $1,176.90   $1,176.90