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 $112.56   5.479%   $118.7272   $118.73   $118.75   $118.70  
  Purchase #2 $81.26   5.848%   $86.0121   $86.01   $86.00   $86.00  
  Purchase #3 $108.28   10.274%   $119.4047   $119.40   $119.40   $119.40  
  Purchase #4 $69.78   5.821%   $73.8419   $73.84   $73.85   $73.80  
  Purchase #5 $216.37   12.650%   $243.7408   $243.74   $243.75   $243.70  
  Purchase #6 $239.75   9.637%   $262.8547   $262.85   $262.85   $262.90  
  Purchase #7 $167.59   12.821%   $189.0767   $189.08   $189.10   $189.10  
  7 purchase totals = $995.59       $1,093.6581   $1,093.65   $1,093.70   $1,093.60