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 $59.35   6.861%   $63.422   $63.42   $63.40   $63.40  
  Purchase #2 $181.98   5.310%   $191.6431   $191.64   $191.65   $191.60  
  Purchase #3 $9.52   5.849%   $10.0768   $10.08   $10.10   $10.10  
  Purchase #4 $248.70   8.417%   $269.6331   $269.63   $269.65   $269.60  
  Purchase #5 $62.64   3.169%   $64.6251   $64.63   $64.65   $64.60  
  Purchase #6 $128.98   6.869%   $137.8396   $137.84   $137.85   $137.80  
  Purchase #7 $106.93   3.587%   $110.7656   $110.77   $110.75   $110.80  
  7 purchase totals = $798.10       $848.0053   $848.01   $848.05   $847.90