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 $109.57   13.152%   $123.9806   $123.98   $124.00   $124.00  
  Purchase #2 $211.86   10.282%   $233.6434   $233.64   $233.65   $233.60  
  Purchase #3 $221.42   8.553%   $240.3581   $240.36   $240.35   $240.40  
  Purchase #4 $31.64   6.397%   $33.664   $33.66   $33.65   $33.70  
  Purchase #5 $181.77   11.139%   $202.0174   $202.02   $202.00   $202.00  
  Purchase #6 $247.96   12.107%   $277.9805   $277.98   $278.00   $278.00  
  Purchase #7 $39.95   11.212%   $44.4292   $44.43   $44.45   $44.40  
  7 purchase totals = $1,044.17       $1,156.0732   $1,156.07   $1,156.10   $1,156.10