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 $212.73   10.156%   $234.3349   $234.33   $234.35   $234.30  
  Purchase #2 $184.69   3.409%   $190.9861   $190.99   $191.00   $191.00  
  Purchase #3 $246.80   6.560%   $262.9901   $262.99   $263.00   $263.00  
  Purchase #4 $60.26   8.349%   $65.2911   $65.29   $65.30   $65.30  
  Purchase #5 $225.67   5.868%   $238.9123   $238.91   $238.90   $238.90  
  Purchase #6 $149.98   3.759%   $155.6177   $155.62   $155.60   $155.60  
  Purchase #7 $10.40   5.745%   $10.9975   $11.00   $11.00   $11.00  
  7 purchase totals = $1,090.53       $1,159.1297   $1,159.13   $1,159.15   $1,159.10