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 $232.87   8.535%   $252.7455   $252.75   $252.75   $252.70  
  Purchase #2 $74.87   13.154%   $84.7184   $84.72   $84.70   $84.70  
  Purchase #3 $99.86   13.289%   $113.1304   $113.13   $113.15   $113.10  
  Purchase #4 $205.57   11.690%   $229.6011   $229.60   $229.60   $229.60  
  Purchase #5 $152.66   8.185%   $165.1552   $165.16   $165.15   $165.20  
  Purchase #6 $75.94   7.744%   $81.8208   $81.82   $81.80   $81.80  
  Purchase #7 $90.28   12.501%   $101.5659   $101.57   $101.55   $101.60  
  7 purchase totals = $932.05       $1,028.7373   $1,028.75   $1,028.70   $1,028.70