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 $54.66   9.394%   $59.7948   $59.79   $59.80   $59.80  
  Purchase #2 $234.93   12.226%   $263.6525   $263.65   $263.65   $263.70  
  Purchase #3 $53.68   5.221%   $56.4826   $56.48   $56.50   $56.50  
  Purchase #4 $22.57   10.809%   $25.0096   $25.01   $25.00   $25.00  
  Purchase #5 $72.44   6.627%   $77.2406   $77.24   $77.25   $77.20  
  Purchase #6 $22.76   7.317%   $24.4253   $24.43   $24.45   $24.40  
  Purchase #7 $22.39   8.820%   $24.3648   $24.36   $24.35   $24.40  
  7 purchase totals = $483.43       $530.9702   $530.96   $531.00   $531.00