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 $203.55   11.621%   $227.2045   $227.20   $227.20   $227.20  
  Purchase #2 $152.33   8.621%   $165.4624   $165.46   $165.45   $165.50  
  Purchase #3 $224.84   11.462%   $250.6112   $250.61   $250.60   $250.60  
  Purchase #4 $32.57   6.106%   $34.5587   $34.56   $34.55   $34.60  
  Purchase #5 $240.56   6.408%   $255.9751   $255.98   $256.00   $256.00  
  Purchase #6 $165.44   3.241%   $170.8019   $170.80   $170.80   $170.80  
  Purchase #7 $143.90   4.268%   $150.0417   $150.04   $150.05   $150.00  
  7 purchase totals = $1,163.19       $1,254.6555   $1,254.65   $1,254.65   $1,254.70