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 $212.43   13.867%   $241.8877   $241.89   $241.90   $241.90  
  Purchase #2 $36.92   4.121%   $38.4415   $38.44   $38.45   $38.40  
  Purchase #3 $185.75   7.372%   $199.4435   $199.44   $199.45   $199.40  
  Purchase #4 $206.42   12.801%   $232.8438   $232.84   $232.85   $232.80  
  Purchase #5 $235.80   4.153%   $245.5928   $245.59   $245.60   $245.60  
  Purchase #6 $43.26   7.771%   $46.6217   $46.62   $46.60   $46.60  
  Purchase #7 $42.52   10.835%   $47.127   $47.13   $47.15   $47.10  
  7 purchase totals = $963.10       $1,051.9580   $1,051.95   $1,052.00   $1,051.80