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 $69.50   11.470%   $77.4717   $77.47   $77.45   $77.50  
  Purchase #2 $54.36   12.587%   $61.2023   $61.20   $61.20   $61.20  
  Purchase #3 $152.79   10.603%   $168.9903   $168.99   $169.00   $169.00  
  Purchase #4 $249.88   10.236%   $275.4577   $275.46   $275.45   $275.50  
  Purchase #5 $166.34   6.523%   $177.1904   $177.19   $177.20   $177.20  
  Purchase #6 $219.91   12.634%   $247.6934   $247.69   $247.70   $247.70  
  Purchase #7 $171.31   3.485%   $177.2802   $177.28   $177.30   $177.30  
  7 purchase totals = $1,084.09       $1,185.2860   $1,185.28   $1,185.30   $1,185.40