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 $247.52   8.668%   $268.975   $268.98   $269.00   $269.00  
  Purchase #2 $210.87   8.401%   $228.5852   $228.59   $228.60   $228.60  
  Purchase #3 $100.70   6.597%   $107.3432   $107.34   $107.35   $107.30  
  Purchase #4 $56.75   10.711%   $62.8285   $62.83   $62.85   $62.80  
  Purchase #5 $232.97   3.450%   $241.0075   $241.01   $241.00   $241.00  
  Purchase #6 $5.52   11.259%   $6.1415   $6.14   $6.15   $6.10  
  Purchase #7 $168.92   9.568%   $185.0823   $185.08   $185.10   $185.10  
  7 purchase totals = $1,023.25       $1,099.9632   $1,099.97   $1,100.05   $1,099.90