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 $179.44   12.801%   $202.4101   $202.41   $202.40   $202.40  
  Purchase #2 $106.33   12.578%   $119.7042   $119.70   $119.70   $119.70  
  Purchase #3 $185.32   8.420%   $200.9239   $200.92   $200.90   $200.90  
  Purchase #4 $84.40   3.496%   $87.3506   $87.35   $87.35   $87.40  
  Purchase #5 $194.75   3.740%   $202.0337   $202.03   $202.05   $202.00  
  Purchase #6 $101.66   11.464%   $113.3143   $113.31   $113.30   $113.30  
  Purchase #7 $201.84   12.284%   $226.634   $226.63   $226.65   $226.60  
  7 purchase totals = $1,053.74       $1,152.3708   $1,152.35   $1,152.35   $1,152.30