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 $176.68   9.718%   $193.8498   $193.85   $193.85   $193.80  
  Purchase #2 $199.48   12.293%   $224.0021   $224.00   $224.00   $224.00  
  Purchase #3 $109.84   9.607%   $120.3923   $120.39   $120.40   $120.40  
  Purchase #4 $235.34   13.814%   $267.8499   $267.85   $267.85   $267.80  
  Purchase #5 $29.64   7.321%   $31.8099   $31.81   $31.80   $31.80  
  Purchase #6 $57.32   7.119%   $61.4006   $61.40   $61.40   $61.40  
  Purchase #7 $247.29   8.372%   $267.9931   $267.99   $268.00   $268.00  
  7 purchase totals = $1,055.59       $1,167.2977   $1,167.29   $1,167.30   $1,167.20