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 $60.37   8.240%   $65.3445   $65.34   $65.35   $65.30  
  Purchase #2 $14.73   10.166%   $16.2275   $16.23   $16.25   $16.20  
  Purchase #3 $134.34   9.129%   $146.6039   $146.60   $146.60   $146.60  
  Purchase #4 $123.28   10.678%   $136.4438   $136.44   $136.45   $136.40  
  Purchase #5 $185.60   8.751%   $201.8419   $201.84   $201.85   $201.80  
  Purchase #6 $220.28   11.577%   $245.7818   $245.78   $245.80   $245.80  
  Purchase #7 $204.45   7.269%   $219.3115   $219.31   $219.30   $219.30  
  7 purchase totals = $943.05       $1,031.5549   $1,031.54   $1,031.60   $1,031.40