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 $185.85   4.363%   $193.9586   $193.96   $193.95   $194.00  
  Purchase #2 $67.52   9.295%   $73.796   $73.80   $73.80   $73.80  
  Purchase #3 $66.38   6.651%   $70.7949   $70.79   $70.80   $70.80  
  Purchase #4 $191.56   8.192%   $207.2526   $207.25   $207.25   $207.30  
  Purchase #5 $133.86   8.411%   $145.119   $145.12   $145.10   $145.10  
  Purchase #6 $189.50   6.672%   $202.1434   $202.14   $202.15   $202.10  
  Purchase #7 $114.57   8.759%   $124.6052   $124.61   $124.60   $124.60  
  7 purchase totals = $949.24       $1,017.6697   $1,017.67   $1,017.65   $1,017.70