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 $25.59   11.704%   $28.5851   $28.59   $28.60   $28.60  
  Purchase #2 $207.53   13.550%   $235.6503   $235.65   $235.65   $235.70  
  Purchase #3 $95.51   12.739%   $107.677   $107.68   $107.70   $107.70  
  Purchase #4 $124.37   6.558%   $132.5262   $132.53   $132.55   $132.50  
  Purchase #5 $199.43   7.603%   $214.5927   $214.59   $214.60   $214.60  
  Purchase #6 $229.79   11.124%   $255.3518   $255.35   $255.35   $255.40  
  Purchase #7 $113.94   3.638%   $118.0851   $118.09   $118.10   $118.10  
  7 purchase totals = $996.16       $1,092.4682   $1,092.48   $1,092.55   $1,092.60