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 $62.42   9.471%   $68.3318   $68.33   $68.35   $68.30  
  Purchase #2 $50.78   4.266%   $52.9463   $52.95   $52.95   $52.90  
  Purchase #3 $158.74   5.691%   $167.7739   $167.77   $167.75   $167.80  
  Purchase #4 $242.72   11.695%   $271.1061   $271.11   $271.10   $271.10  
  Purchase #5 $96.64   10.586%   $106.8703   $106.87   $106.85   $106.90  
  Purchase #6 $175.49   6.193%   $186.3581   $186.36   $186.35   $186.40  
  Purchase #7 $201.79   6.740%   $215.3906   $215.39   $215.40   $215.40  
  7 purchase totals = $988.58       $1,068.7771   $1,068.78   $1,068.75   $1,068.80