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 $248.49   7.621%   $267.4274   $267.43   $267.45   $267.40  
  Purchase #2 $135.31   11.496%   $150.8652   $150.87   $150.85   $150.90  
  Purchase #3 $124.79   8.249%   $135.0839   $135.08   $135.10   $135.10  
  Purchase #4 $34.90   13.336%   $39.5543   $39.55   $39.55   $39.60  
  Purchase #5 $30.36   9.576%   $33.2673   $33.27   $33.25   $33.30  
  Purchase #6 $83.55   12.848%   $94.2845   $94.28   $94.30   $94.30  
  Purchase #7 $218.78   6.831%   $233.7249   $233.72   $233.70   $233.70  
  7 purchase totals = $876.18       $954.2075   $954.20   $954.20   $954.30