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 $221.65   12.263%   $248.8309   $248.83   $248.85   $248.80  
  Purchase #2 $177.99   12.395%   $200.0519   $200.05   $200.05   $200.10  
  Purchase #3 $228.85   12.618%   $257.7263   $257.73   $257.75   $257.70  
  Purchase #4 $22.87   13.560%   $25.9712   $25.97   $25.95   $26.00  
  Purchase #5 $147.36   3.590%   $152.6502   $152.65   $152.65   $152.70  
  Purchase #6 $163.33   9.452%   $178.768   $178.77   $178.75   $178.80  
  Purchase #7 $30.63   4.418%   $31.9832   $31.98   $32.00   $32.00  
  7 purchase totals = $992.68       $1,095.9817   $1,095.98   $1,096.00   $1,096.10