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 $83.33   11.558%   $92.9613   $92.96   $92.95   $93.00  
  Purchase #2 $177.82   13.285%   $201.4434   $201.44   $201.45   $201.40  
  Purchase #3 $43.36   4.371%   $45.2553   $45.26   $45.25   $45.30  
  Purchase #4 $185.60   6.644%   $197.9313   $197.93   $197.95   $197.90  
  Purchase #5 $247.86   7.585%   $266.6602   $266.66   $266.65   $266.70  
  Purchase #6 $155.58   10.642%   $172.1368   $172.14   $172.15   $172.10  
  Purchase #7 $66.42   10.379%   $73.3137   $73.31   $73.30   $73.30  
  7 purchase totals = $959.97       $1,049.7020   $1,049.70   $1,049.70   $1,049.70