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 $70.86   5.759%   $74.9408   $74.94   $74.95   $74.90  
  Purchase #2 $43.48   6.288%   $46.214   $46.21   $46.20   $46.20  
  Purchase #3 $49.28   4.270%   $51.3843   $51.38   $51.40   $51.40  
  Purchase #4 $202.59   6.837%   $216.4411   $216.44   $216.45   $216.40  
  Purchase #5 $54.86   11.123%   $60.9621   $60.96   $60.95   $61.00  
  Purchase #6 $14.61   10.868%   $16.1978   $16.20   $16.20   $16.20  
  Purchase #7 $111.67   5.592%   $117.9146   $117.91   $117.90   $117.90  
  7 purchase totals = $547.35       $584.0547   $584.04   $584.05   $584.00