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 $226.53   11.373%   $252.2933   $252.29   $252.30   $252.30  
  Purchase #2 $118.93   11.688%   $132.8305   $132.83   $132.85   $132.80  
  Purchase #3 $96.47   4.166%   $100.4889   $100.49   $100.50   $100.50  
  Purchase #4 $68.74   9.222%   $75.0792   $75.08   $75.10   $75.10  
  Purchase #5 $242.45   4.344%   $252.982   $252.98   $253.00   $253.00  
  Purchase #6 $239.40   10.372%   $264.2306   $264.23   $264.25   $264.20  
  Purchase #7 $246.72   8.166%   $266.8672   $266.87   $266.85   $266.90  
  7 purchase totals = $1,239.24       $1,344.7717   $1,344.77   $1,344.85   $1,344.80