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 $29.48   10.625%   $32.6123   $32.61   $32.60   $32.60  
  Purchase #2 $77.86   3.760%   $80.7875   $80.79   $80.80   $80.80  
  Purchase #3 $234.72   7.647%   $252.669   $252.67   $252.65   $252.70  
  Purchase #4 $221.66   5.150%   $233.0755   $233.08   $233.10   $233.10  
  Purchase #5 $113.67   9.512%   $124.4823   $124.48   $124.50   $124.50  
  Purchase #6 $155.40   5.562%   $164.0433   $164.04   $164.05   $164.00  
  Purchase #7 $143.37   3.280%   $148.0725   $148.07   $148.05   $148.10  
  7 purchase totals = $976.16       $1,035.7424   $1,035.74   $1,035.75   $1,035.80