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 $211.50   11.588%   $236.0086   $236.01   $236.00   $236.00  
  Purchase #2 $160.57   12.472%   $180.5963   $180.60   $180.60   $180.60  
  Purchase #3 $202.61   10.248%   $223.3735   $223.37   $223.35   $223.40  
  Purchase #4 $228.54   12.346%   $256.7555   $256.76   $256.75   $256.80  
  Purchase #5 $44.90   12.493%   $50.5094   $50.51   $50.50   $50.50  
  Purchase #6 $51.90   10.198%   $57.1928   $57.19   $57.20   $57.20  
  Purchase #7 $100.67   8.360%   $109.086   $109.09   $109.10   $109.10  
  7 purchase totals = $1,000.69       $1,113.5221   $1,113.53   $1,113.50   $1,113.60