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 $240.65   10.150%   $265.076   $265.08   $265.10   $265.10  
  Purchase #2 $246.95   7.870%   $266.385   $266.39   $266.40   $266.40  
  Purchase #3 $138.38   6.697%   $147.6473   $147.65   $147.65   $147.60  
  Purchase #4 $70.95   8.485%   $76.9701   $76.97   $76.95   $77.00  
  Purchase #5 $232.65   4.686%   $243.552   $243.55   $243.55   $243.60  
  Purchase #6 $33.60   10.227%   $37.0363   $37.04   $37.05   $37.00  
  Purchase #7 $190.52   7.591%   $204.9824   $204.98   $205.00   $205.00  
  7 purchase totals = $1,153.70       $1,241.6491   $1,241.66   $1,241.70   $1,241.70