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 $215.29   7.393%   $231.2064   $231.21   $231.20   $231.20  
  Purchase #2 $108.82   9.492%   $119.1492   $119.15   $119.15   $119.10  
  Purchase #3 $22.27   10.582%   $24.6266   $24.63   $24.65   $24.60  
  Purchase #4 $164.85   4.192%   $171.7605   $171.76   $171.75   $171.80  
  Purchase #5 $137.52   9.740%   $150.9144   $150.91   $150.90   $150.90  
  Purchase #6 $239.85   11.525%   $267.4927   $267.49   $267.50   $267.50  
  Purchase #7 $203.73   3.441%   $210.7403   $210.74   $210.75   $210.70  
  7 purchase totals = $1,092.33       $1,175.8901   $1,175.89   $1,175.90   $1,175.80