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 $63.25   3.393%   $65.3961   $65.40   $65.40   $65.40  
  Purchase #2 $228.66   11.278%   $254.4483   $254.45   $254.45   $254.40  
  Purchase #3 $41.52   9.837%   $45.6043   $45.60   $45.60   $45.60  
  Purchase #4 $203.41   7.568%   $218.8041   $218.80   $218.80   $218.80  
  Purchase #5 $206.97   13.589%   $235.0952   $235.10   $235.10   $235.10  
  Purchase #6 $6.41   3.174%   $6.6135   $6.61   $6.60   $6.60  
  Purchase #7 $94.89   12.527%   $106.7769   $106.78   $106.80   $106.80  
  7 purchase totals = $845.11       $932.7384   $932.74   $932.75   $932.70