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 $83.43   13.472%   $94.6697   $94.67   $94.65   $94.70  
  Purchase #2 $130.55   11.346%   $145.3622   $145.36   $145.35   $145.40  
  Purchase #3 $127.66   4.229%   $133.0587   $133.06   $133.05   $133.10  
  Purchase #4 $152.36   13.810%   $173.4009   $173.40   $173.40   $173.40  
  Purchase #5 $164.51   5.308%   $173.2422   $173.24   $173.25   $173.20  
  Purchase #6 $129.42   12.692%   $145.846   $145.85   $145.85   $145.80  
  Purchase #7 $216.79   4.791%   $227.1764   $227.18   $227.20   $227.20  
  7 purchase totals = $1,004.72       $1,092.7561   $1,092.76   $1,092.75   $1,092.80