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 $250.85   6.846%   $268.0232   $268.02   $268.00   $268.00  
  Purchase #2 $200.99   9.324%   $219.7303   $219.73   $219.75   $219.70  
  Purchase #3 $32.79   7.290%   $35.1804   $35.18   $35.20   $35.20  
  Purchase #4 $228.62   9.823%   $251.0773   $251.08   $251.10   $251.10  
  Purchase #5 $119.47   12.847%   $134.8183   $134.82   $134.80   $134.80  
  Purchase #6 $188.47   7.443%   $202.4978   $202.50   $202.50   $202.50  
  Purchase #7 $6.45   3.474%   $6.6741   $6.67   $6.65   $6.70  
  7 purchase totals = $1,027.64       $1,118.0014   $1,118.00   $1,118.00   $1,118.00