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 $184.40   4.560%   $192.8086   $192.81   $192.80   $192.80  
  Purchase #2 $144.64   4.278%   $150.8277   $150.83   $150.85   $150.80  
  Purchase #3 $219.68   9.668%   $240.9187   $240.92   $240.90   $240.90  
  Purchase #4 $6.90   11.674%   $7.7055   $7.71   $7.70   $7.70  
  Purchase #5 $10.27   11.152%   $11.4153   $11.42   $11.40   $11.40  
  Purchase #6 $20.94   9.794%   $22.9909   $22.99   $23.00   $23.00  
  Purchase #7 $20.72   6.277%   $22.0206   $22.02   $22.00   $22.00  
  7 purchase totals = $607.55       $648.6873   $648.70   $648.65   $648.60