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 $212.90   9.319%   $232.7402   $232.74   $232.75   $232.70  
  Purchase #2 $51.51   4.142%   $53.6435   $53.64   $53.65   $53.60  
  Purchase #3 $189.44   6.684%   $202.1022   $202.10   $202.10   $202.10  
  Purchase #4 $57.81   8.293%   $62.6042   $62.60   $62.60   $62.60  
  Purchase #5 $225.45   4.336%   $235.2255   $235.23   $235.25   $235.20  
  Purchase #6 $168.69   11.832%   $188.6494   $188.65   $188.65   $188.60  
  Purchase #7 $168.93   9.362%   $184.7452   $184.75   $184.75   $184.70  
  7 purchase totals = $1,074.73       $1,159.7102   $1,159.71   $1,159.75   $1,159.50