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 $202.88   10.303%   $223.7827   $223.78   $223.80   $223.80  
  Purchase #2 $98.33   10.239%   $108.398   $108.40   $108.40   $108.40  
  Purchase #3 $83.89   9.406%   $91.7807   $91.78   $91.80   $91.80  
  Purchase #4 $193.95   3.782%   $201.2852   $201.29   $201.30   $201.30  
  Purchase #5 $207.99   6.170%   $220.823   $220.82   $220.80   $220.80  
  Purchase #6 $63.74   6.118%   $67.6396   $67.64   $67.65   $67.60  
  Purchase #7 $119.85   13.147%   $135.6067   $135.61   $135.60   $135.60  
  7 purchase totals = $970.63       $1,049.3159   $1,049.32   $1,049.35   $1,049.30