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 $83.59   11.275%   $93.0148   $93.01   $93.00   $93.00  
  Purchase #2 $124.59   10.847%   $138.1043   $138.10   $138.10   $138.10  
  Purchase #3 $148.91   3.175%   $153.6379   $153.64   $153.65   $153.60  
  Purchase #4 $147.95   12.567%   $166.5429   $166.54   $166.55   $166.50  
  Purchase #5 $160.34   11.634%   $178.994   $178.99   $179.00   $179.00  
  Purchase #6 $129.35   7.154%   $138.6037   $138.60   $138.60   $138.60  
  Purchase #7 $181.26   13.659%   $206.0183   $206.02   $206.00   $206.00  
  7 purchase totals = $975.99       $1,074.9159   $1,074.90   $1,074.90   $1,074.80