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 $68.83   7.767%   $74.176   $74.18   $74.20   $74.20  
  Purchase #2 $153.43   7.578%   $165.0569   $165.06   $165.05   $165.10  
  Purchase #3 $84.40   7.424%   $90.6659   $90.67   $90.65   $90.70  
  Purchase #4 $225.88   4.607%   $236.2863   $236.29   $236.30   $236.30  
  Purchase #5 $123.91   9.832%   $136.0928   $136.09   $136.10   $136.10  
  Purchase #6 $29.73   5.703%   $31.4255   $31.43   $31.45   $31.40  
  Purchase #7 $7.62   6.699%   $8.1305   $8.13   $8.15   $8.10  
  7 purchase totals = $693.80       $741.8339   $741.85   $741.90   $741.90