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 $121.77   8.661%   $132.3165   $132.32   $132.30   $132.30  
  Purchase #2 $242.95   3.868%   $252.3473   $252.35   $252.35   $252.30  
  Purchase #3 $38.93   12.168%   $43.667   $43.67   $43.65   $43.70  
  Purchase #4 $174.56   8.443%   $189.2981   $189.30   $189.30   $189.30  
  Purchase #5 $174.42   4.304%   $181.927   $181.93   $181.95   $181.90  
  Purchase #6 $175.35   11.767%   $195.9834   $195.98   $196.00   $196.00  
  Purchase #7 $167.67   4.268%   $174.8262   $174.83   $174.85   $174.80  
  7 purchase totals = $1,095.65       $1,170.3655   $1,170.38   $1,170.40   $1,170.30