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 $180.37   11.768%   $201.5959   $201.60   $201.60   $201.60  
  Purchase #2 $148.93   9.258%   $162.7179   $162.72   $162.70   $162.70  
  Purchase #3 $38.74   8.168%   $41.9043   $41.90   $41.90   $41.90  
  Purchase #4 $22.97   3.737%   $23.8284   $23.83   $23.85   $23.80  
  Purchase #5 $184.81   9.370%   $202.1267   $202.13   $202.15   $202.10  
  Purchase #6 $219.68   12.228%   $246.5425   $246.54   $246.55   $246.50  
  Purchase #7 $235.92   7.273%   $253.0785   $253.08   $253.10   $253.10  
  7 purchase totals = $1,031.42       $1,131.7942   $1,131.80   $1,131.85   $1,131.70