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 $46.77   8.366%   $50.6828   $50.68   $50.70   $50.70  
  Purchase #2 $232.41   3.384%   $240.2748   $240.27   $240.25   $240.30  
  Purchase #3 $20.47   7.668%   $22.0396   $22.04   $22.05   $22.00  
  Purchase #4 $74.78   13.700%   $85.0249   $85.02   $85.00   $85.00  
  Purchase #5 $234.93   3.573%   $243.324   $243.32   $243.30   $243.30  
  Purchase #6 $49.52   8.147%   $53.5544   $53.55   $53.55   $53.60  
  Purchase #7 $150.51   8.200%   $162.8518   $162.85   $162.85   $162.90  
  7 purchase totals = $809.39       $857.7523   $857.73   $857.70   $857.80