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 $54.52   13.717%   $61.9985   $62.00   $62.00   $62.00  
  Purchase #2 $84.29   10.462%   $93.1084   $93.11   $93.10   $93.10  
  Purchase #3 $138.36   9.759%   $151.8626   $151.86   $151.85   $151.90  
  Purchase #4 $193.60   9.870%   $212.7083   $212.71   $212.70   $212.70  
  Purchase #5 $85.39   10.236%   $94.1305   $94.13   $94.15   $94.10  
  Purchase #6 $59.39   4.432%   $62.0222   $62.02   $62.00   $62.00  
  Purchase #7 $12.40   11.345%   $13.8068   $13.81   $13.80   $13.80  
  7 purchase totals = $627.95       $689.6373   $689.64   $689.60   $689.60