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 $87.37   10.427%   $96.4801   $96.48   $96.50   $96.50  
  Purchase #2 $87.50   11.234%   $97.3298   $97.33   $97.35   $97.30  
  Purchase #3 $235.64   11.570%   $262.9035   $262.90   $262.90   $262.90  
  Purchase #4 $127.82   10.481%   $141.2168   $141.22   $141.20   $141.20  
  Purchase #5 $182.65   8.669%   $198.4839   $198.48   $198.50   $198.50  
  Purchase #6 $197.60   7.485%   $212.3904   $212.39   $212.40   $212.40  
  Purchase #7 $225.37   4.467%   $235.4373   $235.44   $235.45   $235.40  
  7 purchase totals = $1,143.95       $1,244.2418   $1,244.24   $1,244.30   $1,244.20