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 $232.44   8.116%   $251.3048   $251.30   $251.30   $251.30  
  Purchase #2 $86.58   10.422%   $95.6034   $95.60   $95.60   $95.60  
  Purchase #3 $120.70   11.516%   $134.5998   $134.60   $134.60   $134.60  
  Purchase #4 $156.39   8.540%   $169.7457   $169.75   $169.75   $169.70  
  Purchase #5 $178.74   9.276%   $195.3199   $195.32   $195.30   $195.30  
  Purchase #6 $234.72   12.465%   $263.9778   $263.98   $264.00   $264.00  
  Purchase #7 $156.28   6.831%   $166.9555   $166.96   $166.95   $167.00  
  7 purchase totals = $1,165.85       $1,277.5069   $1,277.51   $1,277.50   $1,277.50