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 $175.90   4.802%   $184.3467   $184.35   $184.35   $184.30  
  Purchase #2 $232.87   12.783%   $262.6378   $262.64   $262.65   $262.60  
  Purchase #3 $235.58   11.819%   $263.4232   $263.42   $263.40   $263.40  
  Purchase #4 $60.86   12.750%   $68.6197   $68.62   $68.60   $68.60  
  Purchase #5 $249.75   9.439%   $273.3239   $273.32   $273.30   $273.30  
  Purchase #6 $23.48   10.759%   $26.0062   $26.01   $26.00   $26.00  
  Purchase #7 $5.56   3.234%   $5.7398   $5.74   $5.75   $5.70  
  7 purchase totals = $984.00       $1,084.0973   $1,084.10   $1,084.05   $1,083.90