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 $29.92   12.821%   $33.756   $33.76   $33.75   $33.80  
  Purchase #2 $110.70   7.502%   $119.0047   $119.00   $119.00   $119.00  
  Purchase #3 $120.81   5.557%   $127.5234   $127.52   $127.50   $127.50  
  Purchase #4 $154.56   6.686%   $164.8939   $164.89   $164.90   $164.90  
  Purchase #5 $52.97   4.514%   $55.3611   $55.36   $55.35   $55.40  
  Purchase #6 $219.73   5.556%   $231.9382   $231.94   $231.95   $231.90  
  Purchase #7 $27.92   13.357%   $31.6493   $31.65   $31.65   $31.60  
  7 purchase totals = $716.61       $764.1266   $764.12   $764.10   $764.10