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 $17.39   10.177%   $19.1598   $19.16   $19.15   $19.20  
  Purchase #2 $229.53   9.357%   $251.0071   $251.01   $251.00   $251.00  
  Purchase #3 $107.26   9.204%   $117.1322   $117.13   $117.15   $117.10  
  Purchase #4 $243.88   6.235%   $259.0859   $259.09   $259.10   $259.10  
  Purchase #5 $239.46   13.746%   $272.3762   $272.38   $272.40   $272.40  
  Purchase #6 $58.72   11.787%   $65.6413   $65.64   $65.65   $65.60  
  Purchase #7 $37.85   9.787%   $41.5544   $41.55   $41.55   $41.60  
  7 purchase totals = $934.09       $1,025.9569   $1,025.96   $1,026.00   $1,026.00