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 $217.45   6.360%   $231.2798   $231.28   $231.30   $231.30  
  Purchase #2 $181.99   6.753%   $194.2798   $194.28   $194.30   $194.30  
  Purchase #3 $223.86   8.764%   $243.4791   $243.48   $243.50   $243.50  
  Purchase #4 $187.56   12.867%   $211.6933   $211.69   $211.70   $211.70  
  Purchase #5 $189.74   10.314%   $209.3098   $209.31   $209.30   $209.30  
  Purchase #6 $126.38   10.144%   $139.2   $139.20   $139.20   $139.20  
  Purchase #7 $34.68   11.565%   $38.6907   $38.69   $38.70   $38.70  
  7 purchase totals = $1,161.66       $1,267.9325   $1,267.93   $1,268.00   $1,268.00