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 $77.90   12.141%   $87.3578   $87.36   $87.35   $87.40  
  Purchase #2 $243.39   3.307%   $251.4389   $251.44   $251.45   $251.40  
  Purchase #3 $155.47   13.549%   $176.5346   $176.53   $176.55   $176.50  
  Purchase #4 $209.88   8.557%   $227.8394   $227.84   $227.85   $227.80  
  Purchase #5 $65.75   3.178%   $67.8395   $67.84   $67.85   $67.80  
  Purchase #6 $13.96   7.728%   $15.0388   $15.04   $15.05   $15.00  
  Purchase #7 $247.94   8.824%   $269.8182   $269.82   $269.80   $269.80  
  7 purchase totals = $1,014.29       $1,095.8672   $1,095.87   $1,095.90   $1,095.70