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 $58.65   10.383%   $64.7396   $64.74   $64.75   $64.70  
  Purchase #2 $189.98   13.410%   $215.4563   $215.46   $215.45   $215.50  
  Purchase #3 $213.72   6.810%   $228.2743   $228.27   $228.25   $228.30  
  Purchase #4 $242.79   9.301%   $265.3719   $265.37   $265.35   $265.40  
  Purchase #5 $181.32   13.317%   $205.4664   $205.47   $205.45   $205.50  
  Purchase #6 $54.42   10.196%   $59.9687   $59.97   $59.95   $60.00  
  Purchase #7 $36.95   5.541%   $38.9974   $39.00   $39.00   $39.00  
  7 purchase totals = $977.83       $1,078.2746   $1,078.28   $1,078.20   $1,078.40