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 $135.64   11.622%   $151.4041   $151.40   $151.40   $151.40  
  Purchase #2 $225.48   9.379%   $246.6278   $246.63   $246.65   $246.60  
  Purchase #3 $198.52   6.868%   $212.1544   $212.15   $212.15   $212.20  
  Purchase #4 $29.87   7.153%   $32.0066   $32.01   $32.00   $32.00  
  Purchase #5 $45.79   5.483%   $48.3007   $48.30   $48.30   $48.30  
  Purchase #6 $220.97   6.159%   $234.5795   $234.58   $234.60   $234.60  
  Purchase #7 $66.71   4.490%   $69.7053   $69.71   $69.70   $69.70  
  7 purchase totals = $922.98       $994.7784   $994.78   $994.80   $994.80