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 $56.32   8.229%   $60.9546   $60.95   $60.95   $61.00  
  Purchase #2 $213.64   11.808%   $238.8666   $238.87   $238.85   $238.90  
  Purchase #3 $144.50   7.393%   $155.1829   $155.18   $155.20   $155.20  
  Purchase #4 $156.66   8.369%   $169.7709   $169.77   $169.75   $169.80  
  Purchase #5 $198.32   7.619%   $213.43   $213.43   $213.45   $213.40  
  Purchase #6 $42.56   4.641%   $44.5352   $44.54   $44.55   $44.50  
  Purchase #7 $181.56   4.268%   $189.309   $189.31   $189.30   $189.30  
  7 purchase totals = $993.56       $1,072.0492   $1,072.05   $1,072.05   $1,072.10