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 $70.88   8.354%   $76.8013   $76.80   $76.80   $76.80  
  Purchase #2 $167.67   10.638%   $185.5067   $185.51   $185.50   $185.50  
  Purchase #3 $105.90   11.682%   $118.2712   $118.27   $118.25   $118.30  
  Purchase #4 $147.50   9.278%   $161.1851   $161.19   $161.20   $161.20  
  Purchase #5 $180.77   11.741%   $201.9942   $201.99   $202.00   $202.00  
  Purchase #6 $238.31   9.221%   $260.2846   $260.28   $260.30   $260.30  
  Purchase #7 $93.64   5.314%   $98.616   $98.62   $98.60   $98.60  
  7 purchase totals = $1,004.67       $1,102.6591   $1,102.66   $1,102.65   $1,102.70