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 $173.89   12.444%   $195.5289   $195.53   $195.55   $195.50  
  Purchase #2 $8.49   4.687%   $8.8879   $8.89   $8.90   $8.90  
  Purchase #3 $162.40   4.835%   $170.252   $170.25   $170.25   $170.30  
  Purchase #4 $74.64   12.259%   $83.7901   $83.79   $83.80   $83.80  
  Purchase #5 $211.30   11.416%   $235.422   $235.42   $235.40   $235.40  
  Purchase #6 $233.88   13.122%   $264.5697   $264.57   $264.55   $264.60  
  Purchase #7 $160.43   7.517%   $172.4895   $172.49   $172.50   $172.50  
  7 purchase totals = $1,025.03       $1,130.9401   $1,130.94   $1,130.95   $1,131.00