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 $227.33   4.820%   $238.2873   $238.29   $238.30   $238.30  
  Purchase #2 $189.81   9.437%   $207.7224   $207.72   $207.70   $207.70  
  Purchase #3 $23.35   12.573%   $26.2858   $26.29   $26.30   $26.30  
  Purchase #4 $240.94   6.253%   $256.006   $256.01   $256.00   $256.00  
  Purchase #5 $119.28   9.152%   $130.1965   $130.20   $130.20   $130.20  
  Purchase #6 $60.80   13.702%   $69.1308   $69.13   $69.15   $69.10  
  Purchase #7 $10.60   3.462%   $10.967   $10.97   $10.95   $11.00  
  7 purchase totals = $872.11       $938.5958   $938.61   $938.60   $938.60