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 $59.93   6.832%   $64.0244   $64.02   $64.00   $64.00  
  Purchase #2 $113.55   11.268%   $126.3448   $126.34   $126.35   $126.30  
  Purchase #3 $90.37   8.289%   $97.8608   $97.86   $97.85   $97.90  
  Purchase #4 $219.35   5.412%   $231.2212   $231.22   $231.20   $231.20  
  Purchase #5 $243.79   12.466%   $274.1809   $274.18   $274.20   $274.20  
  Purchase #6 $143.70   9.395%   $157.2006   $157.20   $157.20   $157.20  
  Purchase #7 $197.34   10.823%   $218.6981   $218.70   $218.70   $218.70  
  7 purchase totals = $1,068.03       $1,169.5308   $1,169.52   $1,169.50   $1,169.50