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 $216.95   6.797%   $231.6961   $231.70   $231.70   $231.70  
  Purchase #2 $167.37   8.260%   $181.1948   $181.19   $181.20   $181.20  
  Purchase #3 $117.51   5.409%   $123.8661   $123.87   $123.85   $123.90  
  Purchase #4 $174.57   6.849%   $186.5263   $186.53   $186.55   $186.50  
  Purchase #5 $146.82   13.237%   $166.2546   $166.25   $166.25   $166.30  
  Purchase #6 $71.36   9.305%   $78   $78.00   $78.00   $78.00  
  Purchase #7 $45.70   7.668%   $49.2043   $49.20   $49.20   $49.20  
  7 purchase totals = $940.28       $1,016.7422   $1,016.74   $1,016.75   $1,016.80