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 $184.95   8.688%   $201.0185   $201.02   $201.00   $201.00  
  Purchase #2 $189.72   3.806%   $196.9407   $196.94   $196.95   $196.90  
  Purchase #3 $137.95   9.258%   $150.7214   $150.72   $150.70   $150.70  
  Purchase #4 $182.55   4.672%   $191.0787   $191.08   $191.10   $191.10  
  Purchase #5 $47.98   3.408%   $49.6152   $49.62   $49.60   $49.60  
  Purchase #6 $64.48   5.753%   $68.1895   $68.19   $68.20   $68.20  
  Purchase #7 $115.92   12.573%   $130.4946   $130.49   $130.50   $130.50  
  7 purchase totals = $923.55       $988.0586   $988.06   $988.05   $988.00