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 $158.27   12.251%   $177.6597   $177.66   $177.65   $177.70  
  Purchase #2 $183.50   11.144%   $203.9492   $203.95   $203.95   $203.90  
  Purchase #3 $199.94   9.338%   $218.6104   $218.61   $218.60   $218.60  
  Purchase #4 $215.61   11.709%   $240.8558   $240.86   $240.85   $240.90  
  Purchase #5 $5.62   6.642%   $5.9933   $5.99   $6.00   $6.00  
  Purchase #6 $241.61   9.261%   $263.9855   $263.99   $264.00   $264.00  
  Purchase #7 $220.81   10.341%   $243.644   $243.64   $243.65   $243.60  
  7 purchase totals = $1,225.36       $1,354.6979   $1,354.70   $1,354.70   $1,354.70