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 $247.96   8.424%   $268.8482   $268.85   $268.85   $268.80  
  Purchase #2 $139.95   11.229%   $155.665   $155.67   $155.65   $155.70  
  Purchase #3 $226.51   3.697%   $234.8841   $234.88   $234.90   $234.90  
  Purchase #4 $245.80   13.691%   $279.4525   $279.45   $279.45   $279.50  
  Purchase #5 $222.52   9.233%   $243.0653   $243.07   $243.05   $243.10  
  Purchase #6 $130.97   8.363%   $141.923   $141.92   $141.90   $141.90  
  Purchase #7 $219.69   9.864%   $241.3602   $241.36   $241.35   $241.40  
  7 purchase totals = $1,433.40       $1,565.1983   $1,565.20   $1,565.15   $1,565.30