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 $162.55   13.611%   $184.6747   $184.67   $184.65   $184.70  
  Purchase #2 $245.78   3.121%   $253.4508   $253.45   $253.45   $253.50  
  Purchase #3 $130.57   12.559%   $146.9683   $146.97   $146.95   $147.00  
  Purchase #4 $243.99   4.558%   $255.1111   $255.11   $255.10   $255.10  
  Purchase #5 $5.26   12.701%   $5.9281   $5.93   $5.95   $5.90  
  Purchase #6 $64.74   10.344%   $71.4367   $71.44   $71.45   $71.40  
  Purchase #7 $83.39   12.141%   $93.5144   $93.51   $93.50   $93.50  
  7 purchase totals = $936.28       $1,011.0841   $1,011.08   $1,011.05   $1,011.10