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 $177.83   13.184%   $201.2751   $201.28   $201.30   $201.30  
  Purchase #2 $150.45   13.418%   $170.6374   $170.64   $170.65   $170.60  
  Purchase #3 $62.80   4.842%   $65.8408   $65.84   $65.85   $65.80  
  Purchase #4 $45.74   13.321%   $51.833   $51.83   $51.85   $51.80  
  Purchase #5 $245.93   6.591%   $262.1392   $262.14   $262.15   $262.10  
  Purchase #6 $205.72   12.456%   $231.3445   $231.34   $231.35   $231.30  
  Purchase #7 $36.48   4.407%   $38.0877   $38.09   $38.10   $38.10  
  7 purchase totals = $924.95       $1,021.1577   $1,021.16   $1,021.25   $1,021.00