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 $64.69   7.178%   $69.3334   $69.33   $69.35   $69.30  
  Purchase #2 $191.27   11.311%   $212.9045   $212.90   $212.90   $212.90  
  Purchase #3 $101.40   9.675%   $111.2105   $111.21   $111.20   $111.20  
  Purchase #4 $60.59   6.205%   $64.3496   $64.35   $64.35   $64.30  
  Purchase #5 $201.26   12.831%   $227.0837   $227.08   $227.10   $227.10  
  Purchase #6 $198.26   7.459%   $213.0482   $213.05   $213.05   $213.00  
  Purchase #7 $178.94   7.681%   $192.6844   $192.68   $192.70   $192.70  
  7 purchase totals = $996.41       $1,090.6143   $1,090.60   $1,090.65   $1,090.50