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 $52.55   10.279%   $57.9516   $57.95   $57.95   $58.00  
  Purchase #2 $42.41   4.395%   $44.2739   $44.27   $44.25   $44.30  
  Purchase #3 $32.80   12.743%   $36.9797   $36.98   $37.00   $37.00  
  Purchase #4 $235.81   9.222%   $257.5564   $257.56   $257.55   $257.60  
  Purchase #5 $210.96   11.323%   $234.847   $234.85   $234.85   $234.80  
  Purchase #6 $191.86   5.409%   $202.2377   $202.24   $202.25   $202.20  
  Purchase #7 $206.46   4.827%   $216.4258   $216.43   $216.45   $216.40  
  7 purchase totals = $972.85       $1,050.2721   $1,050.28   $1,050.30   $1,050.30