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 $228.29   10.715%   $252.7513   $252.75   $252.75   $252.80  
  Purchase #2 $147.33   13.285%   $166.9028   $166.90   $166.90   $166.90  
  Purchase #3 $25.62   10.619%   $28.3406   $28.34   $28.35   $28.30  
  Purchase #4 $183.81   11.339%   $204.6522   $204.65   $204.65   $204.70  
  Purchase #5 $103.56   7.606%   $111.4368   $111.44   $111.45   $111.40  
  Purchase #6 $58.52   8.504%   $63.4965   $63.50   $63.50   $63.50  
  Purchase #7 $179.58   13.152%   $203.1984   $203.20   $203.20   $203.20  
  7 purchase totals = $926.71       $1,030.7786   $1,030.78   $1,030.80   $1,030.80