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 $88.34   5.869%   $93.5247   $93.52   $93.50   $93.50  
  Purchase #2 $120.31   5.451%   $126.8681   $126.87   $126.85   $126.90  
  Purchase #3 $240.93   6.448%   $256.4652   $256.47   $256.45   $256.50  
  Purchase #4 $68.93   9.503%   $75.4804   $75.48   $75.50   $75.50  
  Purchase #5 $113.77   11.618%   $126.9878   $126.99   $127.00   $127.00  
  Purchase #6 $193.87   7.860%   $209.1082   $209.11   $209.10   $209.10  
  Purchase #7 $168.86   3.801%   $175.2784   $175.28   $175.30   $175.30  
  7 purchase totals = $995.01       $1,063.7128   $1,063.72   $1,063.70   $1,063.80