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 $53.29   13.650%   $60.5641   $60.56   $60.55   $60.60  
  Purchase #2 $218.91   13.145%   $247.6857   $247.69   $247.70   $247.70  
  Purchase #3 $178.47   6.134%   $189.4173   $189.42   $189.40   $189.40  
  Purchase #4 $64.45   11.508%   $71.8669   $71.87   $71.85   $71.90  
  Purchase #5 $246.58   12.815%   $278.1792   $278.18   $278.20   $278.20  
  Purchase #6 $5.79   3.679%   $6.003   $6.00   $6.00   $6.00  
  Purchase #7 $85.25   9.190%   $93.0845   $93.08   $93.10   $93.10  
  7 purchase totals = $852.74       $946.8007   $946.80   $946.80   $946.90