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 $82.93   5.559%   $87.5401   $87.54   $87.55   $87.50  
  Purchase #2 $22.95   11.416%   $25.57   $25.57   $25.55   $25.60  
  Purchase #3 $88.52   8.814%   $96.3222   $96.32   $96.30   $96.30  
  Purchase #4 $81.46   7.225%   $87.3455   $87.35   $87.35   $87.30  
  Purchase #5 $212.56   10.552%   $234.9893   $234.99   $235.00   $235.00  
  Purchase #6 $74.44   8.672%   $80.8954   $80.90   $80.90   $80.90  
  Purchase #7 $50.71   5.351%   $53.4235   $53.42   $53.40   $53.40  
  7 purchase totals = $613.57       $666.0860   $666.09   $666.05   $666.00