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 $153.87   4.638%   $161.0065   $161.01   $161.00   $161.00  
  Purchase #2 $218.31   9.566%   $239.1935   $239.19   $239.20   $239.20  
  Purchase #3 $181.73   12.813%   $205.0151   $205.02   $205.00   $205.00  
  Purchase #4 $26.51   3.395%   $27.41   $27.41   $27.40   $27.40  
  Purchase #5 $39.38   4.697%   $41.2297   $41.23   $41.25   $41.20  
  Purchase #6 $126.96   3.721%   $131.6842   $131.68   $131.70   $131.70  
  Purchase #7 $233.58   9.331%   $255.3753   $255.38   $255.40   $255.40  
  7 purchase totals = $980.34       $1,060.9143   $1,060.92   $1,060.95   $1,060.90