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 $245.96   3.395%   $254.3103   $254.31   $254.30   $254.30  
  Purchase #2 $155.55   5.561%   $164.2001   $164.20   $164.20   $164.20  
  Purchase #3 $6.39   5.208%   $6.7228   $6.72   $6.70   $6.70  
  Purchase #4 $58.55   7.321%   $62.8364   $62.84   $62.85   $62.80  
  Purchase #5 $158.30   11.145%   $175.9425   $175.94   $175.95   $175.90  
  Purchase #6 $158.66   12.524%   $178.5306   $178.53   $178.55   $178.50  
  Purchase #7 $202.65   4.353%   $211.4714   $211.47   $211.45   $211.50  
  7 purchase totals = $986.06       $1,054.0141   $1,054.01   $1,054.00   $1,053.90