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 $188.41   11.436%   $209.9566   $209.96   $209.95   $210.00  
  Purchase #2 $23.35   9.672%   $25.6084   $25.61   $25.60   $25.60  
  Purchase #3 $65.49   9.411%   $71.6533   $71.65   $71.65   $71.70  
  Purchase #4 $245.31   11.294%   $273.0153   $273.02   $273.00   $273.00  
  Purchase #5 $165.51   12.221%   $185.737   $185.74   $185.75   $185.70  
  Purchase #6 $215.46   5.663%   $227.6615   $227.66   $227.65   $227.70  
  Purchase #7 $31.32   6.837%   $33.4613   $33.46   $33.45   $33.50  
  7 purchase totals = $934.85       $1,027.0934   $1,027.10   $1,027.05   $1,027.20