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 $150.49   10.310%   $166.0055   $166.01   $166.00   $166.00  
  Purchase #2 $248.60   13.508%   $282.1809   $282.18   $282.20   $282.20  
  Purchase #3 $26.72   11.785%   $29.869   $29.87   $29.85   $29.90  
  Purchase #4 $158.34   13.613%   $179.8948   $179.89   $179.90   $179.90  
  Purchase #5 $232.93   4.674%   $243.8171   $243.82   $243.80   $243.80  
  Purchase #6 $69.65   8.737%   $75.7353   $75.74   $75.75   $75.70  
  Purchase #7 $41.32   13.223%   $46.7837   $46.78   $46.80   $46.80  
  7 purchase totals = $928.05       $1,024.2863   $1,024.29   $1,024.30   $1,024.30