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 $48.47   6.656%   $51.6962   $51.70   $51.70   $51.70  
  Purchase #2 $229.41   5.198%   $241.3347   $241.33   $241.35   $241.30  
  Purchase #3 $79.44   9.437%   $86.9368   $86.94   $86.95   $86.90  
  Purchase #4 $25.79   12.762%   $29.0813   $29.08   $29.10   $29.10  
  Purchase #5 $174.44   13.261%   $197.5725   $197.57   $197.55   $197.60  
  Purchase #6 $22.45   8.351%   $24.3248   $24.32   $24.30   $24.30  
  Purchase #7 $32.85   12.762%   $37.0423   $37.04   $37.05   $37.00  
  7 purchase totals = $612.85       $667.9886   $667.98   $668.00   $667.90