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 $171.98   3.807%   $178.5273   $178.53   $178.55   $178.50  
  Purchase #2 $30.67   10.770%   $33.9732   $33.97   $33.95   $34.00  
  Purchase #3 $178.79   3.173%   $184.463   $184.46   $184.45   $184.50  
  Purchase #4 $231.59   5.669%   $244.7188   $244.72   $244.70   $244.70  
  Purchase #5 $58.79   6.179%   $62.4226   $62.42   $62.40   $62.40  
  Purchase #6 $88.83   6.594%   $94.6875   $94.69   $94.70   $94.70  
  Purchase #7 $224.45   4.262%   $234.0161   $234.02   $234.00   $234.00  
  7 purchase totals = $985.10       $1,032.8085   $1,032.81   $1,032.75   $1,032.80