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 $37.92   13.527%   $43.0494   $43.05   $43.05   $43.00  
  Purchase #2 $181.83   8.121%   $196.5964   $196.60   $196.60   $196.60  
  Purchase #3 $136.28   9.802%   $149.6382   $149.64   $149.65   $149.60  
  Purchase #4 $184.33   7.415%   $197.9981   $198.00   $198.00   $198.00  
  Purchase #5 $43.80   3.180%   $45.1928   $45.19   $45.20   $45.20  
  Purchase #6 $140.73   3.425%   $145.55   $145.55   $145.55   $145.60  
  Purchase #7 $234.33   13.585%   $266.1637   $266.16   $266.15   $266.20  
  7 purchase totals = $959.22       $1,044.1886   $1,044.19   $1,044.20   $1,044.20