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 $52.93   8.757%   $57.5651   $57.57   $57.55   $57.60  
  Purchase #2 $19.80   11.238%   $22.0251   $22.03   $22.05   $22.00  
  Purchase #3 $177.39   8.850%   $193.089   $193.09   $193.10   $193.10  
  Purchase #4 $31.96   3.353%   $33.0316   $33.03   $33.05   $33.00  
  Purchase #5 $232.48   5.498%   $245.2618   $245.26   $245.25   $245.30  
  Purchase #6 $226.36   9.140%   $247.0493   $247.05   $247.05   $247.00  
  Purchase #7 $238.53   3.475%   $246.8189   $246.82   $246.80   $246.80  
  7 purchase totals = $979.45       $1,044.8408   $1,044.85   $1,044.85   $1,044.80