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 $92.59   10.723%   $102.5184   $102.52   $102.50   $102.50  
  Purchase #2 $29.33   10.286%   $32.3469   $32.35   $32.35   $32.30  
  Purchase #3 $52.79   5.314%   $55.5953   $55.60   $55.60   $55.60  
  Purchase #4 $23.92   11.536%   $26.6794   $26.68   $26.70   $26.70  
  Purchase #5 $52.48   11.338%   $58.4302   $58.43   $58.45   $58.40  
  Purchase #6 $58.31   5.572%   $61.559   $61.56   $61.55   $61.60  
  Purchase #7 $13.35   10.569%   $14.761   $14.76   $14.75   $14.80  
  7 purchase totals = $322.77       $351.8902   $351.90   $351.90   $351.90