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 $79.25   7.189%   $84.9473   $84.95   $84.95   $84.90  
  Purchase #2 $39.42   11.221%   $43.8433   $43.84   $43.85   $43.80  
  Purchase #3 $152.31   9.376%   $166.5906   $166.59   $166.60   $166.60  
  Purchase #4 $156.32   4.745%   $163.7374   $163.74   $163.75   $163.70  
  Purchase #5 $130.95   9.373%   $143.2239   $143.22   $143.20   $143.20  
  Purchase #6 $162.30   6.556%   $172.9404   $172.94   $172.95   $172.90  
  Purchase #7 $219.53   13.663%   $249.5244   $249.52   $249.50   $249.50  
  7 purchase totals = $940.08       $1,024.8073   $1,024.80   $1,024.80   $1,024.60