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 $234.39   11.807%   $262.0644   $262.06   $262.05   $262.10  
  Purchase #2 $112.96   5.623%   $119.3117   $119.31   $119.30   $119.30  
  Purchase #3 $136.97   9.273%   $149.6712   $149.67   $149.65   $149.70  
  Purchase #4 $44.44   3.107%   $45.8208   $45.82   $45.80   $45.80  
  Purchase #5 $225.94   3.450%   $233.7349   $233.73   $233.75   $233.70  
  Purchase #6 $65.94   3.611%   $68.3211   $68.32   $68.30   $68.30  
  Purchase #7 $98.61   11.214%   $109.6681   $109.67   $109.65   $109.70  
  7 purchase totals = $919.25       $988.5922   $988.58   $988.50   $988.60