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 $153.68   13.370%   $174.227   $174.23   $174.25   $174.20  
  Purchase #2 $192.83   6.832%   $206.0041   $206.00   $206.00   $206.00  
  Purchase #3 $37.83   7.806%   $40.783   $40.78   $40.80   $40.80  
  Purchase #4 $163.52   4.566%   $170.9863   $170.99   $171.00   $171.00  
  Purchase #5 $45.71   10.800%   $50.6467   $50.65   $50.65   $50.60  
  Purchase #6 $177.96   13.238%   $201.5183   $201.52   $201.50   $201.50  
  Purchase #7 $216.73   12.115%   $242.9868   $242.99   $243.00   $243.00  
  7 purchase totals = $988.26       $1,087.1522   $1,087.16   $1,087.20   $1,087.10