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 $83.26   6.736%   $88.8684   $88.87   $88.85   $88.90  
  Purchase #2 $112.68   5.192%   $118.5303   $118.53   $118.55   $118.50  
  Purchase #3 $210.86   5.789%   $223.0667   $223.07   $223.05   $223.10  
  Purchase #4 $22.44   8.337%   $24.3108   $24.31   $24.30   $24.30  
  Purchase #5 $54.58   3.790%   $56.6486   $56.65   $56.65   $56.60  
  Purchase #6 $244.87   11.643%   $273.3802   $273.38   $273.40   $273.40  
  Purchase #7 $97.73   10.537%   $108.0278   $108.03   $108.05   $108.00  
  7 purchase totals = $826.42       $892.8328   $892.84   $892.85   $892.80