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 $63.64   8.173%   $68.8413   $68.84   $68.85   $68.80  
  Purchase #2 $146.60   6.726%   $156.4603   $156.46   $156.45   $156.50  
  Purchase #3 $51.51   12.523%   $57.9606   $57.96   $57.95   $58.00  
  Purchase #4 $211.85   11.814%   $236.878   $236.88   $236.90   $236.90  
  Purchase #5 $207.52   13.678%   $235.9046   $235.90   $235.90   $235.90  
  Purchase #6 $96.61   12.696%   $108.8756   $108.88   $108.90   $108.90  
  Purchase #7 $184.77   13.771%   $210.2147   $210.21   $210.20   $210.20  
  7 purchase totals = $962.50       $1,075.1351   $1,075.13   $1,075.15   $1,075.20