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 $245.74   12.187%   $275.6883   $275.69   $275.70   $275.70  
  Purchase #2 $179.29   4.104%   $186.6481   $186.65   $186.65   $186.60  
  Purchase #3 $26.94   11.211%   $29.9602   $29.96   $29.95   $30.00  
  Purchase #4 $167.45   4.769%   $175.4357   $175.44   $175.45   $175.40  
  Purchase #5 $161.79   9.471%   $177.1131   $177.11   $177.10   $177.10  
  Purchase #6 $210.31   3.690%   $218.0704   $218.07   $218.05   $218.10  
  Purchase #7 $18.72   9.190%   $20.4404   $20.44   $20.45   $20.40  
  7 purchase totals = $1,010.24       $1,083.3562   $1,083.36   $1,083.35   $1,083.30