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 $118.93   4.547%   $124.3377   $124.34   $124.35   $124.30  
  Purchase #2 $211.72   11.777%   $236.6543   $236.65   $236.65   $236.70  
  Purchase #3 $209.88   7.457%   $225.5308   $225.53   $225.55   $225.50  
  Purchase #4 $31.46   5.460%   $33.1777   $33.18   $33.20   $33.20  
  Purchase #5 $190.67   4.121%   $198.5275   $198.53   $198.55   $198.50  
  Purchase #6 $198.91   6.141%   $211.1251   $211.13   $211.15   $211.10  
  Purchase #7 $158.52   12.861%   $178.9073   $178.91   $178.90   $178.90  
  7 purchase totals = $1,120.09       $1,208.2604   $1,208.27   $1,208.35   $1,208.20