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 $192.77   12.489%   $216.845   $216.85   $216.85   $216.80  
  Purchase #2 $201.39   11.549%   $224.6485   $224.65   $224.65   $224.60  
  Purchase #3 $191.52   12.644%   $215.7358   $215.74   $215.75   $215.70  
  Purchase #4 $10.38   5.771%   $10.979   $10.98   $11.00   $11.00  
  Purchase #5 $64.74   13.247%   $73.3161   $73.32   $73.30   $73.30  
  Purchase #6 $249.58   8.236%   $270.1354   $270.14   $270.15   $270.10  
  Purchase #7 $152.58   8.215%   $165.1144   $165.11   $165.10   $165.10  
  7 purchase totals = $1,062.96       $1,176.7742   $1,176.79   $1,176.80   $1,176.60