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 $68.30   7.264%   $73.2613   $73.26   $73.25   $73.30  
  Purchase #2 $79.94   10.792%   $88.5671   $88.57   $88.55   $88.60  
  Purchase #3 $223.60   3.530%   $231.4931   $231.49   $231.50   $231.50  
  Purchase #4 $226.67   13.632%   $257.5697   $257.57   $257.55   $257.60  
  Purchase #5 $223.42   9.805%   $245.3263   $245.33   $245.35   $245.30  
  Purchase #6 $75.28   12.410%   $84.6222   $84.62   $84.60   $84.60  
  Purchase #7 $49.61   6.860%   $53.0132   $53.01   $53.00   $53.00  
  7 purchase totals = $946.82       $1,033.8529   $1,033.85   $1,033.80   $1,033.90