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 $164.76   13.263%   $186.6121   $186.61   $186.60   $186.60  
  Purchase #2 $31.45   6.517%   $33.4996   $33.50   $33.50   $33.50  
  Purchase #3 $45.93   9.668%   $50.3705   $50.37   $50.35   $50.40  
  Purchase #4 $81.36   7.695%   $87.6207   $87.62   $87.60   $87.60  
  Purchase #5 $81.26   4.744%   $85.115   $85.12   $85.10   $85.10  
  Purchase #6 $248.83   11.323%   $277.005   $277.01   $277.00   $277.00  
  Purchase #7 $205.40   8.484%   $222.8261   $222.83   $222.85   $222.80  
  7 purchase totals = $858.99       $943.0490   $943.06   $943.00   $943.00