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 $58.48   8.702%   $63.5689   $63.57   $63.55   $63.60  
  Purchase #2 $227.55   8.269%   $246.3661   $246.37   $246.35   $246.40  
  Purchase #3 $244.97   9.464%   $268.154   $268.15   $268.15   $268.20  
  Purchase #4 $207.45   8.582%   $225.2534   $225.25   $225.25   $225.30  
  Purchase #5 $87.31   10.265%   $96.2724   $96.27   $96.25   $96.30  
  Purchase #6 $43.43   12.432%   $48.8292   $48.83   $48.85   $48.80  
  Purchase #7 $138.60   5.258%   $145.8876   $145.89   $145.90   $145.90  
  7 purchase totals = $1,007.79       $1,094.3316   $1,094.33   $1,094.30   $1,094.50