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 $79.29   6.504%   $84.447   $84.45   $84.45   $84.40  
  Purchase #2 $49.38   10.455%   $54.5427   $54.54   $54.55   $54.50  
  Purchase #3 $192.77   5.580%   $203.5266   $203.53   $203.55   $203.50  
  Purchase #4 $23.58   4.773%   $24.7055   $24.71   $24.70   $24.70  
  Purchase #5 $26.73   11.266%   $29.7414   $29.74   $29.75   $29.70  
  Purchase #6 $173.45   13.500%   $196.8658   $196.87   $196.85   $196.90  
  Purchase #7 $181.62   11.218%   $201.9941   $201.99   $202.00   $202.00  
  7 purchase totals = $726.82       $795.8231   $795.83   $795.85   $795.70