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 $53.76   3.734%   $55.7674   $55.77   $55.75   $55.80  
  Purchase #2 $173.35   4.763%   $181.6067   $181.61   $181.60   $181.60  
  Purchase #3 $65.50   13.867%   $74.5829   $74.58   $74.60   $74.60  
  Purchase #4 $126.96   9.156%   $138.5845   $138.58   $138.60   $138.60  
  Purchase #5 $16.59   5.103%   $17.4366   $17.44   $17.45   $17.40  
  Purchase #6 $231.52   11.829%   $258.9065   $258.91   $258.90   $258.90  
  Purchase #7 $167.79   5.199%   $176.5134   $176.51   $176.50   $176.50  
  7 purchase totals = $835.47       $903.3980   $903.40   $903.40   $903.40