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 $189.33   7.313%   $203.1757   $203.18   $203.20   $203.20  
  Purchase #2 $195.49   8.107%   $211.3384   $211.34   $211.35   $211.30  
  Purchase #3 $219.55   11.747%   $245.3405   $245.34   $245.35   $245.30  
  Purchase #4 $60.99   5.127%   $64.117   $64.12   $64.10   $64.10  
  Purchase #5 $225.30   6.369%   $239.6494   $239.65   $239.65   $239.60  
  Purchase #6 $90.42   12.561%   $101.7777   $101.78   $101.80   $101.80  
  Purchase #7 $10.75   11.312%   $11.966   $11.97   $11.95   $12.00  
  7 purchase totals = $991.83       $1,077.3647   $1,077.38   $1,077.40   $1,077.30