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 $87.89   11.102%   $97.6475   $97.65   $97.65   $97.60  
  Purchase #2 $223.49   12.559%   $251.5581   $251.56   $251.55   $251.60  
  Purchase #3 $249.72   9.424%   $273.2536   $273.25   $273.25   $273.30  
  Purchase #4 $145.42   13.731%   $165.3876   $165.39   $165.40   $165.40  
  Purchase #5 $155.78   10.784%   $172.5793   $172.58   $172.60   $172.60  
  Purchase #6 $188.69   9.237%   $206.1193   $206.12   $206.10   $206.10  
  Purchase #7 $140.57   12.376%   $157.9669   $157.97   $157.95   $158.00  
  7 purchase totals = $1,191.56       $1,324.5123   $1,324.52   $1,324.50   $1,324.60