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 $93.84   10.378%   $103.5787   $103.58   $103.60   $103.60  
  Purchase #2 $133.42   9.283%   $145.8054   $145.81   $145.80   $145.80  
  Purchase #3 $216.94   11.231%   $241.3045   $241.30   $241.30   $241.30  
  Purchase #4 $19.45   5.234%   $20.468   $20.47   $20.45   $20.50  
  Purchase #5 $223.84   8.157%   $242.0986   $242.10   $242.10   $242.10  
  Purchase #6 $20.40   11.844%   $22.8162   $22.82   $22.80   $22.80  
  Purchase #7 $216.39   8.821%   $235.4778   $235.48   $235.50   $235.50  
  7 purchase totals = $924.28       $1,011.5492   $1,011.56   $1,011.55   $1,011.60