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 $38.63   7.866%   $41.6686   $41.67   $41.65   $41.70  
  Purchase #2 $223.86   7.122%   $239.8033   $239.80   $239.80   $239.80  
  Purchase #3 $127.36   9.135%   $138.9943   $138.99   $139.00   $139.00  
  Purchase #4 $216.98   11.235%   $241.3577   $241.36   $241.35   $241.40  
  Purchase #5 $84.59   7.728%   $91.1271   $91.13   $91.15   $91.10  
  Purchase #6 $24.36   3.427%   $25.1948   $25.19   $25.20   $25.20  
  Purchase #7 $153.57   8.291%   $166.3025   $166.30   $166.30   $166.30  
  7 purchase totals = $869.35       $944.4483   $944.44   $944.45   $944.50