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 $193.29   9.444%   $211.5443   $211.54   $211.55   $211.50  
  Purchase #2 $64.47   11.453%   $71.8537   $71.85   $71.85   $71.90  
  Purchase #3 $8.41   10.454%   $9.2892   $9.29   $9.30   $9.30  
  Purchase #4 $70.70   3.215%   $72.973   $72.97   $72.95   $73.00  
  Purchase #5 $189.70   6.501%   $202.0324   $202.03   $202.05   $202.00  
  Purchase #6 $51.98   10.266%   $57.3163   $57.32   $57.30   $57.30  
  Purchase #7 $221.93   11.258%   $246.9149   $246.91   $246.90   $246.90  
  7 purchase totals = $800.48       $871.9238   $871.91   $871.90   $871.90