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 $221.45   9.179%   $241.7769   $241.78   $241.80   $241.80  
  Purchase #2 $56.89   12.442%   $63.9683   $63.97   $63.95   $64.00  
  Purchase #3 $114.55   7.427%   $123.0576   $123.06   $123.05   $123.10  
  Purchase #4 $241.92   8.446%   $262.3526   $262.35   $262.35   $262.40  
  Purchase #5 $129.79   9.459%   $142.0668   $142.07   $142.05   $142.10  
  Purchase #6 $159.35   13.843%   $181.4088   $181.41   $181.40   $181.40  
  Purchase #7 $141.87   4.326%   $148.0073   $148.01   $148.00   $148.00  
  7 purchase totals = $1,065.82       $1,162.6383   $1,162.65   $1,162.60   $1,162.80