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 $58.72   6.347%   $62.447   $62.45   $62.45   $62.40  
  Purchase #2 $81.90   13.385%   $92.8623   $92.86   $92.85   $92.90  
  Purchase #3 $215.60   11.809%   $241.0602   $241.06   $241.05   $241.10  
  Purchase #4 $65.72   12.783%   $74.121   $74.12   $74.10   $74.10  
  Purchase #5 $57.84   4.162%   $60.2473   $60.25   $60.25   $60.20  
  Purchase #6 $203.35   6.756%   $217.0883   $217.09   $217.10   $217.10  
  Purchase #7 $108.65   4.850%   $113.9195   $113.92   $113.90   $113.90  
  7 purchase totals = $791.78       $861.7456   $861.75   $861.70   $861.70