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 $233.69   12.829%   $263.6701   $263.67   $263.65   $263.70  
  Purchase #2 $26.58   4.161%   $27.686   $27.69   $27.70   $27.70  
  Purchase #3 $218.78   5.269%   $230.3075   $230.31   $230.30   $230.30  
  Purchase #4 $102.49   6.136%   $108.7788   $108.78   $108.80   $108.80  
  Purchase #5 $212.39   3.114%   $219.0038   $219.00   $219.00   $219.00  
  Purchase #6 $151.29   9.633%   $165.8638   $165.86   $165.85   $165.90  
  Purchase #7 $30.41   11.756%   $33.985   $33.99   $34.00   $34.00  
  7 purchase totals = $975.63       $1,049.2950   $1,049.30   $1,049.30   $1,049.40