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 $220.39   10.563%   $243.6698   $243.67   $243.65   $243.70  
  Purchase #2 $166.91   4.860%   $175.0218   $175.02   $175.00   $175.00  
  Purchase #3 $222.37   6.102%   $235.939   $235.94   $235.95   $235.90  
  Purchase #4 $82.97   6.600%   $88.446   $88.45   $88.45   $88.40  
  Purchase #5 $17.97   6.686%   $19.1715   $19.17   $19.15   $19.20  
  Purchase #6 $226.98   5.347%   $239.1166   $239.12   $239.10   $239.10  
  Purchase #7 $139.49   11.122%   $155.0041   $155.00   $155.00   $155.00  
  7 purchase totals = $1,077.08       $1,156.3688   $1,156.37   $1,156.30   $1,156.30