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 $247.52   11.714%   $276.5145   $276.51   $276.50   $276.50  
  Purchase #2 $172.61   6.802%   $184.3509   $184.35   $184.35   $184.40  
  Purchase #3 $29.64   8.165%   $32.0601   $32.06   $32.05   $32.10  
  Purchase #4 $239.31   8.646%   $260.0007   $260.00   $260.00   $260.00  
  Purchase #5 $122.82   6.703%   $131.0526   $131.05   $131.05   $131.10  
  Purchase #6 $150.87   11.294%   $167.9093   $167.91   $167.90   $167.90  
  Purchase #7 $232.40   8.719%   $252.663   $252.66   $252.65   $252.70  
  7 purchase totals = $1,195.17       $1,304.5511   $1,304.54   $1,304.50   $1,304.70