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 $61.49   12.186%   $68.9832   $68.98   $69.00   $69.00  
  Purchase #2 $213.86   13.834%   $243.4454   $243.45   $243.45   $243.40  
  Purchase #3 $11.42   7.538%   $12.2808   $12.28   $12.30   $12.30  
  Purchase #4 $77.76   12.585%   $87.5461   $87.55   $87.55   $87.50  
  Purchase #5 $155.29   12.760%   $175.105   $175.11   $175.10   $175.10  
  Purchase #6 $158.61   10.496%   $175.2577   $175.26   $175.25   $175.30  
  Purchase #7 $220.76   6.677%   $235.5001   $235.50   $235.50   $235.50  
  7 purchase totals = $899.19       $998.1183   $998.13   $998.15   $998.10