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 $176.27   8.782%   $191.75   $191.75   $191.75   $191.80  
  Purchase #2 $7.29   9.207%   $7.9612   $7.96   $7.95   $8.00  
  Purchase #3 $215.61   6.802%   $230.2758   $230.28   $230.30   $230.30  
  Purchase #4 $69.64   11.137%   $77.3958   $77.40   $77.40   $77.40  
  Purchase #5 $87.34   6.608%   $93.1114   $93.11   $93.10   $93.10  
  Purchase #6 $156.34   4.219%   $162.936   $162.94   $162.95   $162.90  
  Purchase #7 $166.49   7.740%   $179.3763   $179.38   $179.40   $179.40  
  7 purchase totals = $878.98       $942.8065   $942.82   $942.85   $942.90