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 $68.81   6.623%   $73.3673   $73.37   $73.35   $73.40  
  Purchase #2 $193.89   8.695%   $210.7487   $210.75   $210.75   $210.70  
  Purchase #3 $221.71   4.613%   $231.9375   $231.94   $231.95   $231.90  
  Purchase #4 $206.39   9.162%   $225.2995   $225.30   $225.30   $225.30  
  Purchase #5 $103.41   8.700%   $112.4067   $112.41   $112.40   $112.40  
  Purchase #6 $73.84   8.307%   $79.9739   $79.97   $79.95   $80.00  
  Purchase #7 $77.44   3.740%   $80.3363   $80.34   $80.35   $80.30  
  7 purchase totals = $945.49       $1,014.0699   $1,014.08   $1,014.05   $1,014.00