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 $32.90   5.293%   $34.6414   $34.64   $34.65   $34.60  
  Purchase #2 $222.78   11.242%   $247.8249   $247.82   $247.80   $247.80  
  Purchase #3 $85.62   5.322%   $90.1767   $90.18   $90.20   $90.20  
  Purchase #4 $111.40   13.253%   $126.1638   $126.16   $126.15   $126.20  
  Purchase #5 $118.29   5.655%   $124.9793   $124.98   $125.00   $125.00  
  Purchase #6 $191.76   13.827%   $218.2747   $218.27   $218.25   $218.30  
  Purchase #7 $236.31   13.443%   $268.0772   $268.08   $268.10   $268.10  
  7 purchase totals = $999.06       $1,110.1380   $1,110.13   $1,110.15   $1,110.20