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 $117.69   8.497%   $127.6901   $127.69   $127.70   $127.70  
  Purchase #2 $84.39   11.435%   $94.04   $94.04   $94.05   $94.00  
  Purchase #3 $70.66   4.408%   $73.7747   $73.77   $73.75   $73.80  
  Purchase #4 $158.52   13.797%   $180.391   $180.39   $180.40   $180.40  
  Purchase #5 $33.61   8.751%   $36.5512   $36.55   $36.55   $36.60  
  Purchase #6 $202.87   12.216%   $227.6526   $227.65   $227.65   $227.70  
  Purchase #7 $120.86   11.614%   $134.8967   $134.90   $134.90   $134.90  
  7 purchase totals = $788.60       $874.9963   $874.99   $875.00   $875.10