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 $51.83   12.442%   $58.2787   $58.28   $58.30   $58.30  
  Purchase #2 $184.47   6.516%   $196.4901   $196.49   $196.50   $196.50  
  Purchase #3 $173.51   7.621%   $186.7332   $186.73   $186.75   $186.70  
  Purchase #4 $120.28   7.711%   $129.5548   $129.55   $129.55   $129.60  
  Purchase #5 $122.92   5.850%   $130.1108   $130.11   $130.10   $130.10  
  Purchase #6 $147.57   8.376%   $159.9305   $159.93   $159.95   $159.90  
  Purchase #7 $138.40   8.127%   $149.6478   $149.65   $149.65   $149.60  
  7 purchase totals = $938.98       $1,010.7459   $1,010.74   $1,010.80   $1,010.70