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 $24.69   3.347%   $25.5164   $25.52   $25.50   $25.50  
  Purchase #2 $174.84   5.238%   $183.9981   $184.00   $184.00   $184.00  
  Purchase #3 $69.96   4.819%   $73.3314   $73.33   $73.35   $73.30  
  Purchase #4 $219.65   13.837%   $250.043   $250.04   $250.05   $250.00  
  Purchase #5 $212.83   5.165%   $223.8227   $223.82   $223.80   $223.80  
  Purchase #6 $77.98   7.160%   $83.5634   $83.56   $83.55   $83.60  
  Purchase #7 $143.90   9.392%   $157.4151   $157.42   $157.40   $157.40  
  7 purchase totals = $923.85       $997.6901   $997.69   $997.65   $997.60