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 $147.33   13.797%   $167.6571   $167.66   $167.65   $167.70  
  Purchase #2 $223.82   7.546%   $240.7095   $240.71   $240.70   $240.70  
  Purchase #3 $44.61   12.460%   $50.1684   $50.17   $50.15   $50.20  
  Purchase #4 $55.96   8.222%   $60.561   $60.56   $60.55   $60.60  
  Purchase #5 $230.37   5.329%   $242.6464   $242.65   $242.65   $242.60  
  Purchase #6 $49.63   13.203%   $56.1826   $56.18   $56.20   $56.20  
  Purchase #7 $207.72   11.217%   $231.02   $231.02   $231.00   $231.00  
  7 purchase totals = $959.44       $1,048.9450   $1,048.95   $1,048.90   $1,049.00