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 $90.62   5.144%   $95.2815   $95.28   $95.30   $95.30  
  Purchase #2 $150.46   11.135%   $167.2137   $167.21   $167.20   $167.20  
  Purchase #3 $131.67   3.552%   $136.3469   $136.35   $136.35   $136.30  
  Purchase #4 $108.35   4.241%   $112.9451   $112.95   $112.95   $112.90  
  Purchase #5 $73.32   5.781%   $77.5586   $77.56   $77.55   $77.60  
  Purchase #6 $202.40   5.219%   $212.9633   $212.96   $212.95   $213.00  
  Purchase #7 $115.31   4.640%   $120.6604   $120.66   $120.65   $120.70  
  7 purchase totals = $872.13       $922.9695   $922.97   $922.95   $923.00