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 $152.29   8.292%   $164.9179   $164.92   $164.90   $164.90  
  Purchase #2 $49.42   6.347%   $52.5567   $52.56   $52.55   $52.60  
  Purchase #3 $237.62   3.444%   $245.8036   $245.80   $245.80   $245.80  
  Purchase #4 $223.77   6.301%   $237.8697   $237.87   $237.85   $237.90  
  Purchase #5 $62.56   7.404%   $67.1919   $67.19   $67.20   $67.20  
  Purchase #6 $218.45   13.369%   $247.6546   $247.65   $247.65   $247.70  
  Purchase #7 $16.25   7.468%   $17.4636   $17.46   $17.45   $17.50  
  7 purchase totals = $960.36       $1,033.4580   $1,033.45   $1,033.40   $1,033.60