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 $126.48   8.554%   $137.2991   $137.30   $137.30   $137.30  
  Purchase #2 $234.65   13.594%   $266.5483   $266.55   $266.55   $266.50  
  Purchase #3 $31.36   6.658%   $33.4479   $33.45   $33.45   $33.40  
  Purchase #4 $123.74   7.201%   $132.6505   $132.65   $132.65   $132.70  
  Purchase #5 $50.64   3.203%   $52.262   $52.26   $52.25   $52.30  
  Purchase #6 $235.54   11.488%   $262.5988   $262.60   $262.60   $262.60  
  Purchase #7 $45.62   10.743%   $50.521   $50.52   $50.50   $50.50  
  7 purchase totals = $848.03       $935.3276   $935.33   $935.30   $935.30