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 $55.55   11.853%   $62.1343   $62.13   $62.15   $62.10  
  Purchase #2 $180.34   12.825%   $203.4686   $203.47   $203.45   $203.50  
  Purchase #3 $39.26   9.405%   $42.9524   $42.95   $42.95   $43.00  
  Purchase #4 $56.92   10.587%   $62.9461   $62.95   $62.95   $62.90  
  Purchase #5 $246.70   9.418%   $269.9342   $269.93   $269.95   $269.90  
  Purchase #6 $134.49   12.806%   $151.7128   $151.71   $151.70   $151.70  
  Purchase #7 $182.93   11.256%   $203.5206   $203.52   $203.50   $203.50  
  7 purchase totals = $896.19       $996.6690   $996.66   $996.65   $996.60