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 $121.56   4.400%   $126.9086   $126.91   $126.90   $126.90  
  Purchase #2 $240.98   4.382%   $251.5397   $251.54   $251.55   $251.50  
  Purchase #3 $141.80   9.536%   $155.322   $155.32   $155.30   $155.30  
  Purchase #4 $232.39   11.381%   $258.8383   $258.84   $258.85   $258.80  
  Purchase #5 $50.77   3.716%   $52.6566   $52.66   $52.65   $52.70  
  Purchase #6 $64.66   6.647%   $68.958   $68.96   $68.95   $69.00  
  Purchase #7 $88.98   3.540%   $92.1299   $92.13   $92.15   $92.10  
  7 purchase totals = $941.14       $1,006.3531   $1,006.36   $1,006.35   $1,006.30