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 $78.51   8.216%   $84.9604   $84.96   $84.95   $85.00  
  Purchase #2 $120.90   13.763%   $137.5395   $137.54   $137.55   $137.50  
  Purchase #3 $128.77   12.215%   $144.4993   $144.50   $144.50   $144.50  
  Purchase #4 $119.73   6.129%   $127.0683   $127.07   $127.05   $127.10  
  Purchase #5 $212.82   6.191%   $225.9957   $226.00   $226.00   $226.00  
  Purchase #6 $225.71   5.807%   $238.817   $238.82   $238.80   $238.80  
  Purchase #7 $81.70   3.769%   $84.7793   $84.78   $84.80   $84.80  
  7 purchase totals = $968.14       $1,043.6595   $1,043.67   $1,043.65   $1,043.70