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 $59.30   9.755%   $65.0847   $65.08   $65.10   $65.10  
  Purchase #2 $242.77   4.293%   $253.1921   $253.19   $253.20   $253.20  
  Purchase #3 $37.49   6.236%   $39.8279   $39.83   $39.85   $39.80  
  Purchase #4 $24.76   4.269%   $25.817   $25.82   $25.80   $25.80  
  Purchase #5 $127.85   6.249%   $135.8393   $135.84   $135.85   $135.80  
  Purchase #6 $223.28   8.372%   $241.973   $241.97   $241.95   $242.00  
  Purchase #7 $248.82   7.544%   $267.591   $267.59   $267.60   $267.60  
  7 purchase totals = $964.27       $1,029.3250   $1,029.32   $1,029.35   $1,029.30