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 $160.95   8.840%   $175.178   $175.18   $175.20   $175.20  
  Purchase #2 $66.80   9.579%   $73.1988   $73.20   $73.20   $73.20  
  Purchase #3 $65.96   9.257%   $72.0659   $72.07   $72.05   $72.10  
  Purchase #4 $212.45   12.150%   $238.2627   $238.26   $238.25   $238.30  
  Purchase #5 $75.90   12.637%   $85.4915   $85.49   $85.50   $85.50  
  Purchase #6 $149.61   6.416%   $159.209   $159.21   $159.20   $159.20  
  Purchase #7 $24.89   8.591%   $27.0283   $27.03   $27.05   $27.00  
  7 purchase totals = $756.56       $830.4342   $830.44   $830.45   $830.50