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 $86.39   6.806%   $92.2697   $92.27   $92.25   $92.30  
  Purchase #2 $132.54   9.621%   $145.2917   $145.29   $145.30   $145.30  
  Purchase #3 $162.46   6.753%   $173.4309   $173.43   $173.45   $173.40  
  Purchase #4 $86.36   10.310%   $95.2637   $95.26   $95.25   $95.30  
  Purchase #5 $211.43   5.674%   $223.4265   $223.43   $223.45   $223.40  
  Purchase #6 $79.35   11.421%   $88.4126   $88.41   $88.40   $88.40  
  Purchase #7 $188.56   10.853%   $209.0244   $209.02   $209.00   $209.00  
  7 purchase totals = $947.09       $1,027.1195   $1,027.11   $1,027.10   $1,027.10