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 $76.79   12.709%   $86.5492   $86.55   $86.55   $86.50  
  Purchase #2 $169.53   11.546%   $189.1039   $189.10   $189.10   $189.10  
  Purchase #3 $93.74   9.800%   $102.9265   $102.93   $102.95   $102.90  
  Purchase #4 $246.68   5.295%   $259.7417   $259.74   $259.75   $259.70  
  Purchase #5 $80.32   5.833%   $85.0051   $85.01   $85.00   $85.00  
  Purchase #6 $228.62   3.341%   $236.2582   $236.26   $236.25   $236.30  
  Purchase #7 $92.41   10.466%   $102.0816   $102.08   $102.10   $102.10  
  7 purchase totals = $988.09       $1,061.6662   $1,061.67   $1,061.70   $1,061.60